Sunday, January 31, 2010

Evolving Mental Maps

Researchers continue to probe the limits of the brain’s plasticity

We all carry in our heads various mental representations of our body—one example is the wellknown brain map of our sense of touch, sometimes called a homunculus (right). New studies show how such mental maps blur with age and readily extend to accommodate bionic limbs.

Blurred Bodies
As we age, our sense of touch becomes less accurate— some elderly people have a tough time reading Braille, for example. Looking for the roots of this sensory decline, German researchers at Ruhr University Bochum stumbled on a surprise: rather than shriveling up, the brain’s sensory body map—which helps us discriminate Braille letters by determining where the raised bumps are in relation to one another—expands with age, exactly as it does during learning. What could explain this paradox? The homunculus is made up of brain cells that represent our fingers, arms, and so on, loosely tracing a distorted human figurine along the cerebral cortex. In younger people the map stays sharp thanks to cells that dampen neural activity between areas representing different body parts. During aging, however, these cells presumably start to slack off; like an ink drawing that someone spills water on, the contours of the body map start to bleed. Luckily, studies show that a fuzzy old homunculus can be brought back into focus by stimulating the fingertips with a special apparatus, allowing at least some recovery of sensory precision.

Naturally Bionic
To the brain, electronic hardware is no different from flesh and blood, suggests a study at the University of California, Berkeley. In the experiment, monkeys learned to control a computer cursor—a stand-in for a bionic limb—through microelectrodes wiretapping their motor cortex. Although this feat is nothing new, the researchers showed for the first time that a stable memory of the new accessory had formed in the brain. During normal development, a baby learns to control its limbs by creating a mental map of the movable parts of its body—a motor homunculus of sorts. The new finding parallels that process, says neuroscientist Jose Carmena, who led the study, “but it’s about a prosthetic device, and that’s what is profound about it. We’re talking about an extension of your body’s schema.” In other words, once the brain-machine interface gets up to speed, our gray matter might already be set up to achieve effortless, plug-and-play-like control of electronic add-ons. —Frederik Joelving

Source of Information : Scientific American Mind November-December 2009

Saturday, January 30, 2010

Does D Make a Difference?

New studies show low vitamin D levels may impair cognitive function

The push to prevent skin cancer may have come with unintended consequences—impaired brain function because of a deficiency of vitamin D. The “sunshine vitamin” is synthesized in our skin when we are exposed to direct sunlight, but sunblock impedes this process. And although vitamin D is well known for promoting bone health and regulating vital calcium levels—hence its addition to milk—it does more than that. Scientists have now linked this fat-soluble nutrient’s hormonelike activity to a number of functions throughout the body, including the workings of the brain. “We know there are receptors for vitamin D throughout the central nervous system and in the hippocampus,” said Robert J. Przybelski, a doctor and research scientist at the University of Wisconsin School of Medicine and Public Health. “We also know vitamin D activates and deactivates enzymes in the brain and the cerebrospinal fluid that are involved in neurotransmitter synthesis and nerve growth.” In addition, animal and laboratory studies suggest vitamin D protects neurons and reduces inflammation. Two new European studies looking at vitamin D and cognitive function have taken us one step further. The first study, led by neuroscientist David Llewellyn of the University of Cambridge, assessed vitamin D levels in more than 1,700 men and women from England, aged 65 or older. Subjects were divided into four groups based on vitamin D blood levels: severely deficient, deficient, insufficient (borderline) and optimum, then tested for cognitive function. The scientists found that the lower the subjects’ vitamin D levels, the more negatively impacted was their performance on a battery of mental tests. Compared with people with optimum vitamin D levels, those in the lowest quartile were more than twice as likely to be cognitively impaired.

A second study, led by scientists at the University of Manchester in England and published online this past May, looked at vitamin D levels and cognitive performance in more than 3,100 men aged 40 to 79 in eight different countries across Europe. The data show that those people with lower vitamin D levels exhibited slower information processing speed. This correlation was particularly strong among men older than 60 years. “The fact that this relationship was established in a largescale, clinical human study is very important,” Przybelski says, “but there’s still a lot we don’t know.” Although we now know that low levels of vitamin D are associated with cognitive impairment, we do not know if high or optimum levels will lessen cognitive losses. It is also unclear if giving vitamin D to those who lack it will help them regain some of these high-level functions. Because cognitive impairment is often a precursor for dementia and Alzheimer’s disease, vitamin D is a hot topic among Alzheimer’s scientists, who are racing to answer these questions. Przybelski, for example, is planning a study of vitamin D supplements in healthy, normal elderly adults living in an assisted-living community to see if it will affect their incidence of Alzheimer’s in the long term. So how much is enough vitamin D? Experts say 1,000 to 2,000 IU daily—about the amount your body will synthesize from 15 to 30 minutes of sun exposure two to three times a week—is the ideal range for almost all healthy adults. Keep in mind, however, that skin color, where you live and how much skin you have exposed all affect how much vitamin D you can produce. —Diane Welland

Source of Information : Scientific American Mind November-December 2009

Friday, January 29, 2010

Personal Training by Phone

Encouraging physical activity may be as simple as offering small rewards

The promise of a gold star can get grade school students to read more and even take on extra-credit projects. But encouraging positive behavior in adults is more complex, right? Not necessarily, according to recent studies of a mobile phone application called UbiFit. The program, designed by researchers at Intel Research Seattle and the University of Washington, taps into the psychology of motivation by offering seemingly insignificant rewards—graphics of flowers—that people end up striving to attain. UbiFit gathers information from a small, wearable accelerometer to chart an individual’s daily physical activity, tracking various kinds of motion with little input or logging required. Depending on the user’s activity level, flowers of different sizes and colors begin to appear on his or her phone’s background display. In a study conducted this past winter, participants with this “garden” feature from UbiFit had more success maintaining their fitness regimens over the holidays than those whose software simply tracked activity without offering rewards.

Lead researcher Sunny Consolvo, a computer scientist at Intel, read up on classic psychology theories before starting the project. Consolvo suspected that presenting the data in a simple and subtle way would be effective, but even she was surprised by how much the garden graphic seemed to motivate people. “It even worked on me,” she recounts. UbiFit is not yet available for purchase, but other devices exist that similarly use rewards and encouragement to tap into the psychology of motivation [see the review “Boost Your Motivation,” by Melinda Wenner, on page 72]. —Erica Westly

Source of Information : Scientific American Mind November-December 2009

Thursday, January 28, 2010

Risk-Taking Teens Have More Mature Brains

New research finds adultlike structure in the brains of wayward youths

We often hear that teens are irresponsible because their brains are immature. But, contradicting that idea, teen turmoil is completely absent in more than 100 cultures around the world [see “The Myth of the Teen Brain,” by Robert Epstein; Scientific American Mind, April/May 2007]. Nevertheless, neuroscience studies do indeed suggest that the gray matter in the frontal cortex of teens, as compared with adults, is not fully developed. Now a study by neuroscientist Gregory S. Berns and his colleagues at Emory University adds a new wrinkle to the gray matter findings, reporting that teens who are risk takers and drug users actually appear to have a more developed brain than their conservative peers.

The Berns team assessed the risk-taking tendencies of 91 teens between the ages of 12 and 18 with a written test and a drug test. Then, using a relatively new MRI technology called diffusion tensor imaging, the researchers looked at the amount of white matter in the frontal cortex of the teens’ brains. White matter contains the protein myelin, which coats neurons’ spindly axons as they reach toward other areas of the brain. Myelin is important for efficient signaling between neurons, and it is known to grow considerably between childhood and adulthood.

The investigators found that engaging in dangerous behaviors was associated with increased white matter, a result directly opposite to the gray matter findings. One possible interpretation: people whose brains mature early might be more prone to engage in adult activities. But Berns suggests that the entire teen brain idea might be overhyped.
“Nobody denies that the brain develops or that teens take risks,” he says, “but how the two observations got intertwined is beyond me.” Developmental psychologist Laurence Steinberg of Temple University questions the significance of the new study. Other researchers have found a connection between increased white matter and reduced impulsivity, Steinberg explains, which could mean a reduced likelihood of risk taking—the opposite of the Berns finding. Renowned neuroscientist Michael S. Gazzaniga of the University of California, Santa Barbara, is more impressed. “So much for the much touted model of the teenage brain,” Gazzaniga says. “Back to the drawing boards again.” —Robert Epstein

Source of Information : Scientific American Mind November-December 2009

Wednesday, January 27, 2010

Pollution’s Toll on the Brain

Breathing dirty air may have serious effects on cognition, in children and adults

In these days of hybrid cars and carbon credits, it is common knowledge that substances exhaled by autos and coal plants are harmful to our respiratory system. What may be surprising is the degree to which they may harm the brain—in some instances, as much as exposure to lead. A recent string of studies from all over the world suggests that common air pollutants such as black carbon, particulate matter and ozone can negatively affect vocabulary, reaction times and even overall intelligence.

The most recent of these studies found that New York City five-year-olds who were exposed to higher levels of urban air pollutants known as polycyclic aromatic hydrocarbons (PAH) while in the womb exhibited an IQ four points lower than those subjected to less PAH. Alarmingly, “the drop was similar to that seen in exposure to low levels of lead,” says epidemiologist Frederica Perera, director of the Columbia Center for Children’s Environmental Health and head author of the study, in which mothers wore personal air monitors during their pregnancy.

The IQ change was enough of a dip to affect school performance and scores on standardized tests. “These weren’t even superimpressively high levels of pollution,” Perera says. “The levels we measured in our study are comparable to those in other urban areas.” Most PAH pollutants come from motor vehicle emissions, especially diesel- and gas-powered cars and trucks, and from the burning of coal. (Tobacco smoke is another source, so the researchers did not enroll smokers in the study and corrected for secondhand smoke exposure.)

But children’s growing brains are not the only ones affected by this dirty air. A 2008 study in 20- to 50-yearolds conducted jointly by the schools of public health at Harvard University and the University of North Carolina at Chapel Hill pinpointed ozone-related reductions in attention, short-term memory and reaction times equivalent to up to 3.5 to five years of age-related decline. What’s to be done about these brain-harming pollutants? “It’s not a mystery how to reduce them—we need better policies on traffic congestion and technologies for alternative energy and energy efficiency,” Perera says. Fortunately, thereare also more immediate ways to reduce your exposure to the toxic chemicals, such as limiting outdoor physical activity on smoggy days. Ozone alerts and air-quality reports have become a routine part of the morning weather forecast and also appear on sites such as “Depending on where you live, it becomes a good idea to pay attention to air quality before exercising outdoors,” says Lisa Jackson, administrator of the U.S. Environmental Protection Agency. “There is also some benefit to dialing down the intensity if you can’t avoid exercising outside—for example, walking instead of running.” Another smart move: avoid walking, running or bike riding on major streets with heavy bus, truck or car traffic whenever possible, Jackson says. Until emissions controls and other EPA policies begin to significantly impact the levels of traffic-related pollutants in the air around us, bathing our brains in as little of the stuff as possible may be our—and our children’s—best bet. —Sunny Sea Gold

Source of Information : Scientific American Mind November-December 2009

Tuesday, January 26, 2010

Why Success Breeds Success

The brain may not learn from its mistakes after all

Have you ever bowled a string of strikes that seems like it came out of nowhere? There might be more to such streaks than pure luck, according to a study that offers new clues as to how the brain learns from positive and negative experiences. Training monkeys on a two-choice visual task, researchers found that the animals’ brains kept track of recent successes and failures. A correct answer had impressive effects: it improved neural processing and sent the monkeys’ performance soaring in the next trial. But if a monkey made a mistake in one trial, even after mastering the task, it performed around chance level in the next trial— in other words, it was thrown off by mistakes instead of learning from them. “Success has a much greater influence on the brain than failure,” says Massachusetts Institute of Technology neuroscientist Earl Miller, who led the research. He believes the findings apply to many aspects of daily life in which failures are left unpunished but achievements are rewarded in one way or another—such as when your teammates cheer your strikes at the bowling lane. The pleasurable feeling that comes with the successes is brought about by a surge in the neurotransmitter dopamine. By telling brain cells when they have struck gold, the chemical apparently signals them to keep doing whatever they did that led to success. As for failures, Miller says, we might do well to pay more attention to them, consciously encouraging our brain to learn a little more from failure than it would by default.

Source of Information : Scientific American Mind November-December 2009

Monday, January 25, 2010

Related Disorders

Insomnia and depression may arise from common genes

Sleepless nights may be genetically linked to depression, according to new research from the University of Pennsylvania and Virginia Commonwealth University. In a study of twins, researchers found that genetically identical twins who suffered from insomnia were significantly more likely than nonidentical twins to also suffer from depression. The two disorders have been linked before, but the role of genetics has not been clear. The new study indicates that insomnia and depression have overlapping genes, and the next step is to pinpoint those genes through DNA analysis. Possible contenders are the genes related to the neurotransmitters serotonin and norepinephrine, which are involved in both the sleep-wake cycle and mood regulation.

Source of Information : Scientific American Mind November-December 2009

Sunday, January 24, 2010

Reading Minds

Advanced language skills may be essential to predicting others’ thoughts

What’s this guy thinking? Does he know what I know? Most of us develop the ability to make inferences about what other people might be thinking, the hallmark of “theory of mind,” at age four. Scientists have long known that the acquisition of language plays a role in this process, but so far it had been unclear whether social experience could substitute for it. A new study suggests it cannot. Jennie Pyers of Wellesley College and her colleagues studied deaf adults in Nicaragua. Some of the participants had learned an early, rudimentary form of Nicaraguan sign language (NSL), whereas others were fluent in a more sophisticated form of NSL that included mental state terms, such as “know” and “think.” Pyers and her team had all signers undergo a socalled false-belief test in which signers looked at a sequence of pictures showing two boys playing in a room and storing a toy underneath a bed. After one of the boys leaves the room, the other moves the toy to a different location. Study participants then had to choose between two pictures to complete the series: the first showed the returning boy looking for the toy in its original location on reentering the room, and the second showed him looking in its new location. Those Nicaraguans with complex sign language skills were more likely to choose the first picture—indicating an understanding of false belief—than were those with less developed language skills. Moreover, after a two-year period during which early signers improved their NSL knowledge, they performed better at the false-belief task. The findings support the hypothesis that although an implicit understanding of other people’s knowledge and belief states develops early in life, advanced language is needed “to unlock the ability to productively use it,” Pyers says.

Source of Information : Scientific American Mind November-December 2009

Saturday, January 23, 2010

Mental Bottleneck

Our ability to multitask is limited by the prefrontal cortex

Next to the many amazing feats our brain pulls off daily, its inferior ability to juggle a few simple tasks sticks out like a sore thumb. Now research from Vanderbilt University suggests that these limits on multitasking arise from slow processing in the prefrontal cortex, the brain’s central executive. Although the area has been known to be involved in multitasking, its exact role is a matter of debate. Using functional MRI, the researchers found that when people were juggling two assignments, their prefrontal cortex appeared to deal with the tasks one by one—creating that familiar mental bottleneck—instead of processing them in parallel as do sensory and motor parts of the brain. With training the prefrontal activation time became shorter, cranking up the speed of the mental conveyor belt by about 10 times. Unfortunately, the researchers note, the benefits of training might not apply to tasks other than those specifically practiced. “It’s not like you become able to multitask [with drills]; it’s just that you become able to do each task very quickly,” says cognitive neuroscientist Paul Dux, now at the University of Queensland in Australia, who conducted the experiment.

Source of Information : Scientific American Mind November-December 2009

Friday, January 22, 2010

Wide-Reaching Effects

The brain’s plasticity is even greater than suspected

The idea that the adult brain changes with experience was once a radical idea, but it is now well accepted that certain areas—say, the motor cortex, when learning a new physical skill—can grow new neurons or create stronger connections.

Now scientists report that the brain is even more mutable than suspected. Thanks to an unconventional research technique, neuroscientists have found the first physical proof that new experiences and information have wide-ranging effects throughout both hemispheres of the brain, rather than just creating connections in one discrete area.

The story begins in the hippocampus, the area of the brain associated with shortterm memory. In the past, researchers have electrically stimulated slices of disembodied hippocampus and seen how stimulation changes the structure of nearby neurons. But the new study took a different tack. Led by Santiago Canals, a biological cyberneticist currently at the Institute of Neurosciences in Alicante, Spain, the team set aside the dissected hippocampi in favor of a more true-tolife approach. After implanting electrodes in live rats, the group used a combination of functional MRI, electroencephalography (EEG) and microstimulation— triggering nerve cells with small doses of electric current—to trace in real time what happened to neuronal structures in the rats’ brains when neurons in the hippocampus were stimulated. In contrast to studying the slices, this method allowed the scientists to see what happened in the hippocampus in context with what was going on all over the brain—like comparing a 2-D drawing of a bedroom with a 3-D rendering of the whole house.

“We have learned that what we call neuronal plasticity isn’t exclusive to individual synapses or even the neurons where they contact but rather occurs throughout the functional network in which synapses and neurons are embedded,” Canals says. “Those networks are absent in brain slices, so they couldn’t be studied before.”

By showing how activity in the hippocampus causes widespread changes in brain structure, Canals says the findings could explain why new memories are at first dependent on the hippocampus but can eventually be recalled without triggering that part of the brain at all.

Source of Information : Scientific American Mind November-December 2009

Thursday, January 21, 2010

Bring Your Fat to a Checkup

Your weight, BMI, and body-fat percentage provide some important clues about your overall health, but they’re far from definitive. For more comprehensive information, it’s time to doctor up.

Yes, you may hate waiting in the doctor’s office. And you probably aren’t crazy about stripping off your clothes and donning a paper gown that’s roughly the width of two paper towels. But your family doctor is an important team player in every aspect of your body’s health. If your weight has been creeping up and you’re starting to get nervous about the possible ill effects, your doctor can run some of the following tests:

• Cholesterol levels. Doctors measure two types of cholesterol. At high levels, LDL cholesterol can clog your arteries when it forms into a sticky plaque. HDL cholesterol is the good stuff—it helps mop up excess LDL cholesterol, keeping your arteries clean. To stay healthy, you need a balance between these two players. A blood test can tell you how your body is doing.

• Triglyceride level. Triglycerides are a form of fat that travels through your bloodstream. Your body uses triglycerides to move fat from one spot to another, so it can fuel the work going on in your body. But if there’s too much fat circulating in your blood, you’re at greater risk for heart disease. Once again, you can check your triglycerides with a blood test.

• High blood glucose. Normally, the human body is extremely effective at pulling excess sugar out of your blood using insulin. But if this sugar-storage system is starting to malfunction—perhaps after a lifetime on the Krispy Kreme diet—your blood will stay sugared-up. This is the beginning of diabetes. Left unchecked, the runaway sugar can damage your heart, eyes, and kidneys.

• Blood pressure. Blood pressure measures the force of your blood as it pushes through your arteries (page 161). Although high blood pressure causes no immediate damage (and has virtually no obvious symptoms), over time it strains your heart and thickens your arteries. Left untreated, it can lead to organ damage, heart attack, or stroke.

Even if you have an ideal BMI and aren’t worrying about your weight, there are reasons you might still want to take these tests. For example, you might have a family history of early heart disease, smoke two fistfuls of cigarettes between breakfast and lunch, or have unexplained symptoms. If in doubt, chat it up at your next physical.

Source of Information : Oreilly - Your Body Missing Manual

Wednesday, January 20, 2010

Do-It-Yourself Fat Measurement

A body-fat scale (which looks like your average bathroom scale, but measures electric conductance instead of weight) is the most affordable, practical way for you to keep an eye on your fat without getting help from someone else. But even top-rated scales make so many assumptions that you can’t trust the number they give you. So does that make them a gargantuan waste of time?

Not necessarily—provided you use your body-fat scale to measure changes in body fat.
Used this way, a body-fat scale lets you judge the success of an exercise plan or the toll of an expanding waistline. To use this strategy, you need to make sure you get a consistent reading. Here are some tips that can help:

• Watch your water intake. The amount of water in your body can dramatically change the reading of a body-fat scale. The best idea is to measure your body fat at the same time of day, at least one hour after drinking or eating, and definitely not after exercise. Consider making it part of your morning routine.

• Adjust the settings. For example, many scales have a specific profile for athletes or children. If you pick the right settings, the scale is more likely to make the right assumptions for your body and give you a more accurate reading.

• Don’t compare people. You and your friend may use the same scale, but it’s not fair to compare the numbers. Minor differences between the two of you can skew the results in different ways. Similarly, it doesn’t make sense to compare your own readings on different body-fat scales.

• Get a baseline. If you get the chance, measure your body fat with a more reliable method—for example, a skinfold test or an underwater weighing—then compare that result with the reading on your scale to figure out a basic frame of reference for how accurate your scale is.

Source of Information : Oreilly - Your Body Missing Manual

Tuesday, January 19, 2010

Body-Fat Percentage

If you’re concerned about good health, your sheer poundage isn’t nearly as important as finding out how much of you is made up of fat. In other words, you need to spend less time thinking about your weight and BMI, and more time concentrating on your body-fat percentage—the weight of your fat compared to the total weight of your body.

Everyone has a certain amount of essential fat stored in small amounts in organs, bone marrow, muscles, and the nervous system. This fat supports the normal functioning of these systems. Women have a bit more fat in the breast, pelvis, hips, and thighs, which is a prerequisite to making babies. Along with this bare minimum, it’s important to have at least a little more fat to use as an energy reserve, so you don’t collapse the next time you skip breakfast.

Unfortunately, the only place you can get a foolproof measure of your body-fat percentage is on an autopsy table. Some other techniques are nearly as good, but require the work of professionals and expensive hospital equipment. A few are much less accurate, but can be carried out at home. Here’s a quick roundup of the ways to measure your body fat:

• Imaging. An MRI (magnetic resonance imaging) machine can peer under your skin to create shocking scans that show the amount and distribution of your body fat.

• Hydrostatic weighing. Some specialized laboratories (and a few health clubs) have water tanks that are designed for underwater weighing. This technique works because fat isn’t nearly as dense as muscle and bone (which is why well-padded people float more easily). Using a bit of math, you can combine your underwater weight with your normal weight to get a fairly accurate measurement of your body-fat percentage.

• Skinfold measurements. To perform this test, a professional painstakingly pinches the folds of fat in various places on your body using calipers. It’s not particularly accurate, and it doesn’t sound like anybody’s idea of a fun Friday night. However, it works well if you just want to monitor changes in your body fat, as long as you get the same person to administer the measurement each time.

• Electrical conductance. This test sends a faint current through your body, calculates your body’s electrical resistance, and uses the result to estimate your body-fat percentage. This works because muscle contains a lot of water, and so conducts electricity quite well, while fat does not. This technique is used in hospital-grade equipment that costs tens of thousands of dollars, and in cheapie department-store versions, which look like ordinary digital scales.

Source of Information : Oreilly - Your Body Missing Manual

Monday, January 18, 2010

Body Mass Index

One common, but somewhat crude, measure for assessing your poundage is the body mass index, or BMI. Oddly enough, the BMI was created by a Belgian mathematician (perhaps concerned about overindulging on the chocolate delicacies of his countrymen). In any case, the BMI became a surprisingly popular and somewhat controversial way to separate the thin from the fat. To calculate your BMI, you divide your height (in meters) by your weight (in kilograms). Or, you can plug more common pound and inch measurements into this version of the formula:

BMI = weight (lb) * 703 / ( (height * height) (in * in) )
This gives you a single number that ranks your weight. For example,
if you’re five feet eight inches tall (that’s 68 inches total) and weigh 180
pounds, your BMI is 27.4. According to the standard BMI groupings, that
puts you into the overweight category.

If you don’t want to pull out your pocket calculator, you can use one of the many BMI calculators online (just search for “BMI”). Or you can find your spot on the handy BMI chart shown, which helps you judge exactly where you fall in your weight class.

The BMI has some known weak spots. For instance, short, muscular types and athletes can end up in the obese zone even though they’re in prime condition. Similarly, elderly folks can coast through with a normal ranking if they have high body fat combined with very little muscle weight.

Despite these weaknesses, the BMI is good for two things:

• Making conclusions about a population. For example, if the BMI suggests that one-third of Americans are dangerously obese (as it does), the odds are that very few of them are muscular athletes in the prime of their lives.

• Giving a rough idea of the weight situation for an ordinary person. If you fall far outside the normal zone, the BMI is giving you a red warning flag. It’s up to you to follow up and see if you really do have the weight problem it suggests. The standard next step is to measure your waist and analyze your blood.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Sunday, January 17, 2010

The Lessons of Fat Cells

Finding out the secret rules of fat cells is fascinating, but does it do you any good? The obvious hope (both for failed dieters and pharmaceutical executives) is that this understanding will lead to a drug that can control appetite or fat storage. In the meantime, you can learn a few things from your fat cells:

• Hold the line on childhood eating. No one knows why different people gain different numbers of fat cells throughout childhood and adolescence. However, there’s at least a possibility that environmental influences are at work, meaning early binging habits might tune the body to a lifetime of calorie craving. So if you’re a parent, make every effort to provide a varied, healthy diet for your child—one that’s rich in fruits and vegetables, and low in processed foods—and resist the temptation to teach “clean your plate” or “food is your reward” lessons. Even if your efforts don’t influence your child’s fat cell count, they’ll help set down lifetime habits that can defend against the worst dietary excesses.

• Expect diets to be difficult. Because a diet can’t change your fat-cell count, you’ll always have the potential to regain the weight you lose. To give yourself the best odds of staying slim, start by dieting small (with a goal of losing 10 pounds at a time), then concentrate on maintaining your weight and adjusting to a new lifestyle.

• Don’t moralize fat. While it’s a biological fact that fat people get fat by eating too much, none of us is completely in control of the powerful drive to eat. Those with a larger collection of fat cells just might start life with the odds stacked against them.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Saturday, January 16, 2010

The Life and Death of a Fat Cell

As you’ve seen, fat cells are like miniature people—the more fat you feed them, the more they plump up. Unfortunately, even the strictest diet can’t remove them. Instead, it leaves you with billions of slimmed-down fat cells crying out for another meal.

But there’s another side to this story. Different people do have different numbers of fat cells. Not only do obese people have dramatically bigger fat cells than slim people, they often have many more. For years, scientists have wondered what causes these differences. Do fat cells ever die? Does something trigger the creation of new fat cells? Is it our fault?

In 2008, a group of scientists devised a clever experiment to answer these questions. It worked by examining the effect of nuclear-bomb explosions on human fat cells. At first glance, this sounds like a Very Bad Idea. After all, detonating nuclear bombs— even in the name of science—is likely to put off the ethics board. But here’s the trick: the researchers didn’t launch the bombs themselves. Rather, they took advantage of a bit of Cold War history to track radioactive carbon in human fat cells.

Now you’re probably wondering what radioactive carbon is doing in human fat cells, and that’s a reasonable question. The obvious answer is“because the researchers put it there,” but it turns out they aren’t allowed to do that, either. (It’s likely to be toxic.) The experiment was launched, unknowingly, by the American and Soviet militaries when they tested nuclear bombs. These tests sent large amounts of radioactive carbon into the atmosphere that drifted to all corners of the world. Plants pulled it out of the atmosphere, animals ate the plants, and we ate the animals. The end result is that the U.S. and Soviet governments radioactively labeled pretty much everyone who was around at the time.

Here’s a chart that shows how the levels of radioactive carbon soared during nuclear testing and rapidly diminished when nuclear testing went underground in 1963.

By matching the level of radioactive carbon in the air with the amount of it in the DNA of a fat cell (along with a generous pinch of statistical mojo), researchers can figure out when that cell was created. It’s as though each fat cell has its own “manufactured on” date.

To draw their conclusions, the researchers analyzed fat extracted from about 700 people. Here’s what they found:

• The number of fat cells grows through childhood and adolescence, but stabilizes sometime in late adolescence. After that, your fat-cell count stays the same.

• People on the fast track to obesity pack on their fat cells more quickly in childhood and stop producing them around age 16 or 17. Naturally thin people have fewer fat cells, but keep producing them until the age of 18 or 19.

• Even extreme events—for example, dramatic weight loss through surgery or super-sized weight gain—change the size of fat cells in the body, but don’t nudge the number. (That said, many experts believe years of excessive weight gain that lead to hundreds of extra pounds will eventually cause fat cells to multiply.)

• About 10 percent of your fat cells die and are replaced each year, whether you’re thin, fat, or somewhere in between.

No one knows why some people end adolescence with more fat cells than others. There’s a good case to be made that it’s hard-coded in your genes (in other words, blame mom and dad). Events during fetal development and childhood might also play a role—for example, chowing down on calorie-rich food early in life could kick off certain processes in your body, preparing it for a life of fat retention. But no matter the reason, it’s clear that some people enter adulthood set up for caloric challenges, with a big family of fat cells. They won’t necessarily gain weight more easily than a naturally lean person, but they’ll probably feel a stronger pull toward that second batch of chocolate chip cookies.

To put it another way: fat people are doing something wrong. But they’re doing it because their bodies are telling them to.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Friday, January 15, 2010

The Secret Power of Fat

The connection between fat and hormones is at the forefront of fat research. In the past, scientists assumed that the problems caused by excess fat were the result of its physical burden. They worried that fat would strain bones and joints, plug up arteries, and crush internal organs. But today, many scientists believe that the chemical contribution of fat is more important—and far more dangerous. Although the hormones that fat secretes are critically important in small doses, in large amounts they can trigger runaway inflammation, confuse other organs, and throw off your body’s regulatory processes.

Here’s an example: Osteoarthritis is a painful condition that causes the cartilage in your joints to break down. Studies find that as your body weight creeps up, your risk for osteoarthritis rises along with it. The traditional explanation is that excess weight causes extra wear and tear to important joints like your knees, which is certainly possible. However, increased body weight also increases the likelihood of osteoarthritis in places where weight isn’t all that significant, like your hands. A more recent explanation is that excess fat triggers chemical changes that can wreak havoc on your body (for example, inflammation that attacks the cartilage in your hands).

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Thursday, January 14, 2010

Big Fat Myths

Fat is always on our minds. We waste many productive hours thinking about the fat that’s on our plate, our bodies, other people’s bodies, and (for purely scientific reasons) the bodies of scantily clad celebrities on the Internet. Other body parts don’t come close to getting this much attention, which is probably why fat is the subject of a messy collection of mistakes, myths, and misinformation. Here are some fat factoids you might have encountered:

• Muscle turns to fat. Muscle and fat are different types of tissue, and the body can’t convert one to the other any more than you can transform a pear into a chocolate truffle. However, your fat sits on top of your muscles, which means that a small weight gain can quickly mask those six-pack abs.

• A calorie is a calorie. There are a dizzying range of factors that can influence how well your body transforms food into energy and (ultimately) fat, from the quality of the bacteria in your digestive tract to the combination of nutrients in the food you eat. So-called experts that miss this subtlety warn that a single extra glass of juice a day can add up to dozens of pounds of weight gain over a year, which is clearly nonsense. Other than paranoid dieters, no one eats with such maniacal precision. The truth is that the body is miraculously successful at preserving its preferred weight.

• Thin people have faster metabolisms. This is partly true, in the sense that naturally thin people often expend more energy in small, natural ways (for example, with constant fidgeting). However, people of all body types appear to burn calories in roughly the same proportion to their weight, which means that obese people actually need faster metabolisms to maintain their extra poundage. However, there’s one huge exception: If you start an extreme diet, your metabolism will fight you, slowing itself down to a calorie-conserving crawl. Similarly, pig out in an effort to put on pounds, and your metabolism will speed up to keep you at your current weight.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Wednesday, January 13, 2010

How Fat Controls Your Body

Your body has billions of fat cells. (For example, people with healthy, normal weight carry around some 40 billion fat cells.) Each one is a miniature reservoir for storing fat. Fat cells work in a rather unusual way. When your body squirrels away fat, your fat cells don’t do what you might expect them to—multiply. Instead, they gobble up the extra fat, inflating themselves like rubber balloons. In fact, if you take a close-up look at a fat cell under a microscope, you find that nearly the entire cell is filled with a greasy droplet of fat. The rest of the cell—the cellular machinery that runs the shop—is squeezed to the very edge of the cell, and much more difficult to spot. Early researchers wondered if fat cells actually did any work on their own, or if their squashed functional parts were completely disabled.

Fat cells make up a spongy type of tissue that biologists call adipose tissue. Inside this tissue, your body packs fat cells together in a neat, almost honeycombed pattern. It’s like bubble wrap for your body.

In the past, scientists thought fat cells were simply boring blobs of lard. We now know that they don’t hang around idly—instead, they release massive quantities of hormones that have effects throughout your body. For this reason, many fat scientists (er, make that scientists studying fat) argue that fat isn’t just excess tissue—it’s a smart and powerful organ in its own right.

At this point, it’s natural to ask what these fat-secreted hormones are up to. Although the interaction between fat cells and the rest of your body is fantastically complex, here are some key examples:

• Female fertility. As women know, carrying and delivering a baby is a body-straining odyssey. Without a bare minimum of fat, your body won’t even let you try. If your body decides that you don’t have the necessary fat reserves to live through a pregnancy and nourish a baby, you’ll stop menstruating. Regain the fat, and the deal’s back on.

• Appetite. Fat cells release a hormone called leptin that tells your brain to damp down feelings of hunger. Leptin is often blamed for the nearly inevitable weight gain that follows severe dieting. As you lose fat, your leptin level falls and your brain feels less satisfied, becoming much more likely to trigger a late-night cheesecake craving.

• Regulating the immune system. Fat cells release compounds that fire up parts of your immune system. Too much fat, and these signals get amplified to harmful levels, triggering inflammation deep inside your body. This inflammation can damage your body and lead to other conditions, like heart disease, arthritis, and type 2 diabetes. On the other hand, elite athletes who eat an extremely low-fat diet—say, ultra-marathon runners—end up suppressing their immune systems and becoming more susceptible to infection.

Hormones are special chemicals the body uses to send messages from one place to another. Your fat releases hormones into your blood, where it can travel to other body parts, like your brain.

It might seem that a little extra leptin would make a great diet pill. Unfortunately, it doesn’t work that way. The problem is that your body is far more interested in preventing starvation than in fighting weight gain. If your leptin level rises, your brain adapts to this new level and considers it the “new normal.” Then, when you stop taking the pills and your leptin level falls, hunger quickly sets in. This process, like much of the body’s appetite-control system, is a bit biased. In fact, it looks a lot like a one-way street to more eating.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Tuesday, January 12, 2010


It can strike fear in the heart of the most level-headed, body-positive person. Wrapping your body just under its outer covering of skin is a gentle, gelatinous blanket of fat. Serving as insulation, cushioning, an energy reserve, and the focus of intense social scrutiny, fat is one body component that the average person spends more effort to remove than to understand. But fat is no lightweight—although it gets a lot of bad press, it’s as essential to your survival as any of your more popular organs.

Fat is also at the heart of a controversial body mystery. Unlike the fine tuned processes in the rest of your body, fat storage is the one mechanism that frequently goes completely off the rails. In the process, excessive fat sets up ordinary people for a dismal collection of health troubles.

It’s hard to overstate just how big the problem is. Compared with other animals, obese humans are biological wonders—pound for pound, the fattest creatures on earth. (If you aren’t already feeling self-conscious, consider this: The percentage of body fat of the fattest humans tops that of even the generously proportioned beluga whale.) Still more remarkable is just how common excessive fat is. Despite billions of dollars, high-powered research, and some seriously good intentions, people are getting fatter year after year, in countries across the globe. In the U.S., more than a third of the population is overweight and another third is obese, leaving less than a third of the population to give everyone else disapproving looks in line at the all-you-can-eat restaurants. Clearly there’s something about the modern world that’s throwing the body’s carefully tuned mechanisms seriously out of whack.

You’ll start to unravel this riddle. You’ll learn why you need fat, how it works, and why your body is so keen to hold on to every ounce of fat it’s got. You’ll also measure your body-fat percentage and learn some techniques that can help you battle excess weight. Along the way, you’ll explore some common questions, like: Do diets really work? Who’s to blame for your bulging belly? And why do some people struggle to count calories while others can down an entire cheesecake and get away scot-free?

The Purpose of Fat
Fat elicits contradictory emotions. Oh, we like it well enough when it coats our fish sticks, but it’s not nearly as appealing when it’s wrapped around our midriffs. And even though fat’s a visceral part of us, we treat it as an unwelcome intruder. Consider how most well-adjusted people can agree with both of these statements:

Every part of the human body is good, proper, and has its own beautiful purpose.

Fat is an evil, evil thing, and I’d do anything to eliminate it.

But before you call the local liposuction clinic, consider this: Fat—a modest amount of it, anyway—is your friend.

The fat in your body cushions your organs and joints, absorbing shocks and protecting them from damage. It also insulates your body against temperature extremes. Less critically, body fat gives you a cushion to sit on and covers hard bone with padding, making hugs much more pleasant. The fat in your diet helps your body absorb certain vitamins, produces compounds that regulate blood clotting and inflammation, and builds structures like cell membranes. Your brain is literally filled with the stuff— by weight, your brain’s more than half fat.

Most important, fat is the body’s energy storage system. In times of plenty, your body stores extra calories as fat, ensuring that none of the effort you spend cooking, chewing, and digesting goes to waste. When food is scarce, your body taps into its fat reserves, burning them to fuel everything your cells do.

This energy storage system kept our distant ancestors alive through tough times and countless famines, while the nibblers and picky eaters perished. The problem is that famines don’t come along as often as they used to. As a result, average people spend most of their lives planted firmly in the first part of the energy-storage equation, hoarding fat for food shortages that never come.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Monday, January 11, 2010

The Psychology of Comb-Overs

The comb-over is a hair-grooming practice in which a balding man brushes a few strands of hair over a wide expanse of his bald head, usually starting with an unnatural part. Sometimes he cements the hair in place with oil or a styling product. The hallmark of a comb-over is that the combed-over hair covers only a small portion of the available scalp area. Much as a piece of avant-garde music might call attention to the silences between successive notes, a comb-over directs your helpless attention to the hair that is no longer there.

Comb-overs are a somewhat mysterious phenomenon. Although most men find them distasteful, many still end up adopting them in later years of baldness. Sociological thinkers (and people with a great deal of extra time on their hands) suggest that combover practitioners fall prey to the sorites paradox. Essentially, the sorites paradox describes how small steps that seem sensible on their own can lead to an absurd outcome. In the case of comb-overs, the victim may begin moving the part of his hair by a small amount to add fullness to a region of thinning hair. Only as the process of baldness accelerates does this become a futile attempt to hide a glaring patch of skin under the last few stragglers of hair. Incidentally, the Japanese call men with comb-overs barcode men, because the lines of neatly aligned hair resemble barcode symbols.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Sunday, January 10, 2010

Hair Growth and Hair Loss

Your hair follicles have a tiring job, and every once in a while they take a break. At the moment, roughly 90 percent of the hair on your head is growing, while the rest is taking some time off. Some of that hair will resume growing again after a pause of a week or two. A smaller proportion will simply fall out—about 50 hairs a day. But don’t panic, because the same hair follicle will begin creating a new hair in its place. An average hair takes six years of abuse on your head before it drops out and the hair follicle starts over. Eyebrows and eyelashes have a different growing schedule. Eyebrow hairs grow for about 10 weeks, and then rest for the better part of a year. (This is what makes eyebrow shaving such a dastardly revenge tactic.) Eyelash hairs last about three months apiece before falling out and being replaced.

Hair growth is an issue that comes with a boatload of baggage. Hair embarrasses us when it appears in certain places (inside our ears, for example). In other places, it mortifies us when it vanishes. But other than cutting your hair, you have little control over its comings and goings.

Here are some quick facts that can help separate the bare facts from the follicle folklore:
• Hair doesn’t grow faster or thicker after you shave it (on any part of your body).

• Hair doesn’t grow faster at night. Female hair doesn’t grow faster during menstruation. Instead, all hair grows at a constant rate with a brief resting period.

• Frequent washing, blow drying, and dyeing your hair doesn’t destroy hair follicles or slow hair growth. However, these activities might make your current hair more brittle and fragile. But even if you damage a hair to the point of falling out, the same hair follicle will produce a new one to take its place.

• You’re born with all the hair follicles you’ll ever have. As you grow and your skin stretches from infant-sized to adult proportions, your hair follicles simply become more spread out.

• While you’re pregnant, each hair clings on a little bit longer, eventually giving you a fuller head of hair. After you give birth, your body sheds its hair more quickly to make up for lost time.

• The only ways to remove hair permanently are laser hair removal and electrolysis. Both treatments take numerous sessions over the course of many months, and neither treatment works for all people or all hair.

• Wearing hats doesn’t cause hair loss.

Male-pattern baldness, which causes the infamous ring-around-the-baldspot effect, develops gradually and eventually affects about two-thirds of all men. Its causes are genetic, and its treatments are few. A small set of medications give some improvement to some people, but these drugs are often ineffectual. There are only two guaranteed solutions: hair-transplant operations (which are expensive, time-consuming, and may look odd, since hair loss continues around the transplanted patches), and head shaving. If you opt for the latter, you’ll likely tell people that you deliberately chose baldness to emphasize your virile, youthful manliness. Everyone will know the truth, of course, but they’ll also be quietly relieved that you aren’t practicing the dreaded comb-over.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Saturday, January 9, 2010

Hair's Shampoo and Conditioner

Few products make the bold, imaginative, and highly delusional claims that shampoos and conditioners do. Almost every brand describes mystical powers that can revitalize, energize, volumize, and therapize hair (and the last two aren’t even real words).

Unfortunately, the science of hair pours some distinctly unsudsy water on the whole idea. Because each one of your hairs is a sorry strand of dead material, there’s really nothing you can do to “nourish” it. That means you don’t need to shampoo with vitamins or amino acids. The best botanicals are the ones you grow in pots and water twice a week, and you’re better off rubbing herbs and fruit extracts on your dinner than on your scalp.

And forget other hair-care health claims—the government doesn’t regulate shampoo, so manufacturers don’t need to substantiate their fanciful promises. (For example, some shampoos boast that they protect hair from ultraviolet rays. This typically means that the manufacturer has added a UV-protective ingredient, which you’ll only end up rinsing down the drain, and which isn’t present in strong enough concentrations to have an effect in the first place.)

The truth of the matter is that shampoo provides a rather straightforward hair-cleaning service. To understand how it works, you need to know how your hair gets dirty in the first place. Ordinarily, the same sebum that lubricates your skin moisturizes your hair. This is mostly a good thing, because the thin layer of oil protects your hair from damage. But as the hours pass and you go about your daily business, your hair collects natural oil and skin flakes that shed from your scalp. This is where shampoo comes in—it includes powerful surfactants that dissolve these substances, in much the same way that you rinse dirt out of clothes with detergent or grease out of pots with dish soap. The problem is that, in the process, shampoo strips out most of the sebum, leaving your hair dry and fragile (although the effect is far gentler than if you showered with laundry detergent or dish soap).

To balance this effect, many shampoos have conditioning agents, and many people use a separate conditioning product. There’s a bit more variability to the way that conditioners work, but essentially they all aim to coat the hair shaft with protective sebum-like compounds. Some creamy conditioners feel heavy in the hair and glue together damaged fibers and loose scales. Other conditioners are lighter and oilier. But all these substances cling to the hair shaft and don’t rinse out with plain water.

The best hair-care advice for a biology wonk is this: Don’t break your budget on high-end products. Buy the shampoo that matches your hair type (oily or dry) and use conditioner to manage excessive dryness. Finally, don’t pressure yourself into washing your hair every day. If you’re just as happy waiting a day or two, your dead hair will probably be a bit better off.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Friday, January 8, 2010


Along with the different sweat glands and oil glands, there’s one more type of body equipment rooted in the dermis—your hair.

Hair consists of long, flexible strands of dead cells. These cells are filled with keratin, the same wonder substance that strengthens the outer layers of your skin. As you can see, the surface of the hair shaft consists of overlapping scales, like shingles on a roof.

This close-up holds the secret to hair frizz. On a humid day, tiny water droplets work their way in between the scales of the hair shaft, making the hair thicker and rougher. Conditioners try to prevent the problem by leaving an oily, water-repelling coating on the hair. Some anti-frizz products accomplish the same thing using silicone, which simultaneously seals the hair and weighs it down, straightening it.

Your body creates each hair in a hair follicle— a tiny pouch deep in your dermis, where your hair is woven together out of living cells. As each new layer of cells is tacked onto the bottom of the hair, the cells die, and the hair becomes just a little bit longer. In other words, your body treats your hair the same way it treats your skin—it keeps the living cells on the inside and puts the dead stuff on the outside. Which is good in a way, because a head full of living hair would make for an agonizing day at the barbershop.

Your hair stores a permanent record of the toxins you ingest, including illegal drugs like cocaine, amphetamines, heroin, and marijuana. A standard hair drug test searches for traces of drugs consumed over the last 90 days. But take longer strands of hair or some slow-growing body hair and you can easily put the last year of your life under the microscope.

Vellus Hair
Compared to other animals, humans appear relatively hairless. But the surprising truth is that you have more hair follicles crammed onto each square inch of your skin than the hairiest chimpanzee, monkey, or gorilla. The difference is that most of your hair (whether you’re a man or a woman) is nearly invisible. It consists of a fine, slow-growing, almost colorless covering of downy hair called vellus hair. Vellus hair blankets your body, insulating your skin and heightening your sensitivity to touch. It’s the reason you can sometimes “feel” a person moving past you in a darkened room—the passing air currents disturb your fine hairs and trigger the sensitive nerves attached to them. However, vellus hair is easily overlooked and nearly invisible without a magnifying glass. It’s sometimes known as “peach fuzz.”

Terminal Hair
Terminal hair is the more obvious hair found on your body, including the hair on your head, your eyebrows, and your eyelashes. After puberty, terminal hair appears in many more places on your body—some where it’s wanted, and some where it’s decidedly inconvenient.

Terminal hair is thicker, longer, and darker than vellus hair, although some individuals can have light-colored and fine terminal hair. Terminal hair also boasts a range of textures and colors. The difference between wavy, curly, and straight hair is all in the shape of the follicle that produces it. For example, a perfectly round follicle constructs straight hair, while an oval follicle produces wavy hair. All the hair-care products in the world can’t alter the shape of your follicles.

Like most of your body’s equipment, terminal hair has good reasons for existing:

• The terminal hair on your eyelashes keeps dirt and insects out of your eyes. Your ear hairs and nose hairs play a similar role. The terminal hair on your eyebrows • prevents sweat and rain from dripping onto your face.

• On your head, terminal hair helps prevent sunburns on sunny days and heat loss on cold ones.

• Pubic hair is a type of terminal hair that serves as a secondary sexual characteristic. That means it’s there to advertise that you’re a fully functioning adult with the appropriate baby-making abilities.

And, of course, humans have picked up the habit of using hair for something entirely different—as a powerful expression of self-identity that can announce everything from your gender to your political affiliation.

Source of Information : Oreilly - Your Body Missing Manual (08-2009)

Thursday, January 7, 2010

Deodorants and Antiperspirants

When people learn how body odor works, the first question they usually ask is how they can stop it. The first line of defense is bathing, which reduces your sweaty residue, leaving bacteria with a whole lot less to lunch on. However, soap and water won’t kill the bacteria itself, which is a more-or-less permanent resident on your body.

Another popular tactic is to use deodorant or antiperspirant, which you usually apply to bacteria’s favorite dining spot—the underarms. These two products work differently. Deodorants mask body odor (which should rightly be called bacteria odor) with a different smell. They may also contain powders that absorb moisture and chemicals that can kill some of the bacteria. Because you can never completely eradicate the bacteria, deodorant is really a population-control tactic.

Antiperspirants may include musky perfumes and germicides like deodorants, but they also have an aluminum-based chemical that temporarily blocks sweat glands. To be labeled an antiperspirant, clinical tests must show that the product actually works. This involves rather amusing studies that put a number of people in very hot rooms and get lab technicians to collect the resulting sweat. The rule of thumb is that a basic antiperspirant must reduce underarm sweating by 20 percent in most people. A highpowered antiperspirant (one with “maximum” or similar language on the label) must hit the 30-percent mark. Prescription antiperspirants can reduce sweating even more.

Now that you understand the science of your armpit, you’re ready to learn about a significant drawback to antiperspirants: They only work on the comparatively harmless eccrine glands. So while antiperspirants do decrease the amount of wetness (which does slow down your armpit bacteria), they can’t suppress the strong-smelling apocrine glands. So, after an hour at the gym, you’ll still smell like, well, yourself.

Finally, it’s important to address one of the very real risks of antiperspirants. No, it’s not breast cancer or Alzheimer’s disease, despite what you might have read in imaginative email chain letters. For the record, aluminum, the key ingredient in antiperspirants, is the third most common element on our planet, and it’s found in food, air, and over-the-counter medications like antacids, all of which provide more aluminum than you can absorb from an antiperspirant through your skin. Furthermore, the amount of waste your sweat glands excrete is small, so there’s no reason to think that slowing down a few sweat glands can increase the level of toxins in your blood.

The real danger of antiperspirants is staining. That’s because the aluminum can react with your sweat to create an embarrassing yellowish stain on your favorite clothes. If this is a problem, apply your antiperspirant and walk around shirtless until it dries. Or consider switching to deodorant.

Deodorants and antiperspirants are simple ways to deal with ordinary sweat, but if you suffer from excessive sweating, you may need the help of the medical community. Your doctor can determine if your sweating is linked to another problem, such as thyroid disease, or if it’s just genetic bad luck (in which case you have a range of treatment options, from stronger antiperspirants to underarm Botox injections and surgery). Lastly, look out for body-odor changes. For example, suddenly sweet body odor may hint at diabetes, or it could just be the result of a change in diet. If in doubt, have it checked.

Source of Information : Oreilly - Your Body Missing Manual

Wednesday, January 6, 2010

Do Humans Have Pheromones?

In many other animals, smells are an important signaling mechanism that can indicate ownership and trigger mating. When chemicals have this effect, they’re called pheromones. Essentially, pheromones act like hormones that travel out of the body. An individual secretes pheromones, they waft through the air, and they trigger a behavior in someone else.

Despite some top-flight scientific studies and many teenage fantasies, no one has ever discovered a chemical in humans that acts like a pheromone. However, there are plenty of tantalizing possibilities. Some provocative scientists suggest that pheronomes may underlie the mysterious chemistry of mate selection and explain why we tend to choose lovers who have distinctly different immune systems from our own. Others wonder if pheromones can explain why women living together may begin to menstruate on the same schedule. Both of these phenomena are highly disputed and might add up to nothing more than hot air. However, the possibility of mysterious chemicals controlling our destinies is thought-provoking. It’s also enough to make you think twice before reaching for the deodorant stick.

Source of Information : Oreilly - Your Body Missing Manual

Tuesday, January 5, 2010

Body Odor

So far, we’ve skirted over one nagging question—namely, why does your personal air conditioner smell like dirty socks? Surprisingly, sweat itself has no odor. You can douse yourself in the stuff without picking up the faintest scent. However, the bacteria that live on your skin aren’t so innocent—they feed on your sweat and produce a rich collection of stinky substances. (This is the reason a discarded workout shirt smells worse the next day—the bacteria living on it have had some extra time to digest its tasty payload.)

As you’ve probably noticed, body odor seems to emanate from specific places in your body. To understand why, you need to recognize that your body actually has two types of sweat gland:

• Eccrine. These are the most numerous sweat glands. They’re found all over your body and are particularly dense on the palms of your hands, the soles of your feet, and on your forehead. The eccrine glands do most of your body’s temperature control.

• Apocrine. These sweat glands are concentrated in the forested areas— the armpits and genitals. Instead of secreting ordinary salt water, they squirt out a thick, milky fluid that has plenty of fats and proteins.

Apocrine glands almost always dump their contents onto a hair follicle. Unlike eccrine sweat glands, apocrine glands don’t do much for temperature control, and they react more readily to emotions and sexual stimulation. Bacteria devour rich, apocrine sweat, leaving their signature gamey odors behind. Bacteria aren’t nearly as interested in the watery sweat that leaks out of the eccrine glands, but under the right conditions they can still make a meal of it, along with skin oils and dead skin cells. (That’s why a warm, moist, poorly ventilated foot can develop a room-clearing odor that rivals the sweatiest armpit.)

This raises an excellent question—if apocrine glands don’t help you cool your body, why are they there stinking up the place? It seems that the chief purpose of apocrine sweat is to create your distinctive body odor. Several studies have shown that women, when asked to smell a lineup of used undershirts, can pick out their man’s shirt by smell. Thus, apocrine glands are the human equivalent of the sexual-scent glands of other animals— and whether they have a real effect or are just an evolutionary leftover depends on whom you ask.

Apocrine glands develop during puberty, which is why babies and toddlers don’t have body odor problems.

Source of Information : Oreilly - Your Body Missing Manual

Monday, January 4, 2010

How Fingerprints Work

Living on the wrong side of the law? If so, you’ll want to spend some time thinking about fingerprints, the unique pattern of whorled ridges that adorns every human’s fingertips. Your fingerprints were formed, more or less at random, while you were still in your mother’s womb. To biologists, fingerprints are known as friction ridges, and they’re thought to improve our sense of touch. They might also give you a better grip on small, wet objects. And thanks to your sebaceous glands and your sweat glands, your fingerprints leave wet, oily tracks wherever they’ve been, which is of great interest to law-enforcement officers. Incidentally, there’s no shortage of exquisitely painful home-cooked approaches to alter or remove your friction ridges, including sandpaper, Super Glue, needles, and liquid nitrogen. Unsurprisingly, you can find all of these distinctly dimwitted ideas on the Internet. But before you try them out, consider investing in a pair of latex gloves instead. After all, when police interview suspects, they pay particular attention to the fellow with no fingerprints.

Source of Information : Oreilly - Your Body Missing Manual

Sunday, January 3, 2010

How Much Heat Do You Lose Through Your Head?

It’s an often-repeated, slightly wonky story. Cover your head on a cold day, because 40 percent of your body heat exits through your cranium. Or 60 percent. Or 80 percent. Sure, the explanations are a bit dubious—the skin on your scalp is extremely thin, heat rises, and if you’re wearing clothes the heat has nowhere else to go—but who can question such an enduring yarn?

Serious-minded scientists have pointed out that if the 60 percent figure were true, you’d be more comfortable on an Alaskan cruise with nothing on but a ski hat than if you were fully dressed but bare-headed. So perhaps it’s no surprise to find that the true figure is somewhat less than 10 percent. In fact, you lose little more heat out of your head than you lose from any similarly sized part of your body, although your face, head, and chest are more sensitive to temperature changes, which may give you the impression that you’re colder.

This confusion might have resulted from a flawed interpretation of a military study that examined heat loss in fully dressed soldiers. The soldiers were bundled up in survival suits, but hatless, so their heads did account for about half of the heat they lost. (If they war-gamed naked, the equation would change.) In any case, a hat remains a sensible addition to any cold-weather ensemble.

Source of Information : Oreilly - Your Body Missing Manual

Saturday, January 2, 2010

Your Temperature Control System

In some respects, the life of a reptile has a lot of appeal. When the sun rises on a Monday morning, springing out of bed is the last thing on any lizard’s mind. Much as you may need a second or third cup of coffee before you can string a coherent sentence together, a lizard can’t do much of anything until it’s spent a long, lazy morning basking in the sun, heating its body to operating temperature.

Warm-blooded humans like you don’t work that way. Your internal temperature stays at a balmy 98.6 degrees Fahrenheit (or thereabouts). This is quite a feat, because your body continuously generates heat—primarily by your muscles contracting during routine activity and by major organs like the liver. To cool down, your body needs to release some of that heat into the air around you.

Using a design that’s the human equivalent of a hot-water radiator, your body sends warm blood to the surface of your skin so it can radiate heat away to the cooler world outside. When you need to conserve heat, your body clamps down on this process, tightening the blood vessels in your skin. That reduces the flow of blood near the skin and slows your rate of heat loss.

This system explains why people become flushed when they’re hot (it’s from the increased blood flow). It also explains how frostbite inflicts its damage. The cold itself doesn’t harm your body—instead, the extremely reduced blood flow starves your cells of the oxygen they need to survive.

One thing this system doesn’t explain is the uniquely human habit of blushing, in which sudden embarrassment causes increased blood flow and pronounced reddening, particularly in the face. Scientists guess that blushing may be an involuntary skin signal designed to solve social problems. It works like this: If you get into a sticky situation with a more dominant member of your social tribe, blushing expresses your remorse and gets you off the hook without the need for physical violence. Experts agree that the best way to deal with blushing is to announce it and accept it (for example, by saying something along the lines of, “Oh drat, I’m about to blush again!”). Trying to hide it usually triggers a cycle of increased embarrassment and increased blushing, turning the skin of a sensitive person to a distinct shade of cranberry jelly.

The body’s heat-exchange system makes perfect sense, but on its own it’s just not enough. Sure, your body can radiate heat through your skin, but on a hot day it won’t lose a sufficient amount to keep you cool. To lose heat more efficiently, you need the help of sweat.
Sweat is part of your body’s messy air-conditioning unit. Your body sweats continuously, but you don’t notice the small amounts of moisture that trickle out because it’s truly miniscule, and your body reabsorbs some of it. But when the outside temperature rises or the activity in your body soars (say, when you run to catch the last bus home), your body ramps up its sweat production.

Sweat is mostly water, with a pinch of salt and tiny amounts of other waste products thrown in. As sweat evaporates, it takes some of the heat from your skin, noticeably cooling it. (And if you don’t think it’s noticeable, try taking a hot shower and then walk around the house without drying yourself.)

But the real point of sweat isn’t to cool your skin, but to cool your blood, thereby maintaining your internal body temperature. To accomplish this, your body uses the blood redirection trick you saw on page 24. When you sweat, your body sends more blood to the newly cooled surface of your skin. The blood gets a chance to cool down, and then it gets pumped back deeper into your body. This isn’t all that different from the way a refrigerator works—it circulates a special substance (ammonia gas) through coils at the back. Once this substance cools, it’s returned to the inside of the fridge so it can keep your rutabagas fresh.

Your skin is studded with several million sweat glands. They cover every square inch of your skin, with just a few exceptions (namely, your lips, nipples, and sexual equipment). The structure of a sweat gland is simple: It looks like a coiled tube that sits in the dermis (where your body produces sweat) and opens out through a pore. Some, but not all, sweat glands squirt their liquid out onto a hair, like your sebaceous glands do. If you live in a cold or moderate climate, you can produce about one quart of sweat every hour. Move to the tropics and a few weeks later your body doubles or triples its maximum sweatproducing capacity. At the same time, your sweat becomes less salty.

Stress also causes sweating. Other than the obvious purpose (to embarrass you in your third-grade public-speaking competition), sweating in response to stress works as part of your body’s fight-or-flight response. Essentially, your body assumes that you’re either going to run away from or attack the threat in front of you, so it prepares for the imminent increase in body heat by switching on your natural air conditioning.

Say what you like about farm animals and zoo dwellers, but humans are the undisputed sweating champions of the natural world. In fact, many mammals barely sweat at all. Cats and dogs, for example, sweat only on their paws. (This is why dogs pant—they can’t cool themselves sufficiently by sweating alone. The air they inhale cools the surface of their lungs and the blood that runs nearby.) Our habit of sweating probably explains why we don’t have thick fur covering our bodies like some other animals—if we did, it would interfere with our ability to evaporate sweat from our skin.

Source of Information : Oreilly - Your Body Missing Manual

Friday, January 1, 2010


Less helpfully, sebaceous glands cause acne, the scourge of teenagers everywhere. The problem starts when puberty ramps up the production of certain hormones, most significantly, testosterone (in both boys and girls). At the first sign of these hormones, the highly excitable sebaceous glands begin pumping out huge quantities of sticky sebum. Inevitably, they clog themselves up. But the real nightmare is that they keep producing sebum even when the glands are blocked, causing a swelling that eventually appears on the surface of the skin as a whitehead. With chronic acne, swollen sebaceous glands become inflamed, and trapped sebum can form a cyst. Cysts, in turn, can lead to permanent scarring.

So a blockage deep in a sebaceous gland causes acne, which itself is usually caused by the sudden onrush of hormones at puberty. It’s just as important to note what doesn’t cause acne, including chocolate, fried foods, and poor hygiene. (In fact, aggressive washing can exacerbate the inflammation.) Stress may make acne worse, which is rather unfair, considering that the stress was probably caused by the monster zit that appeared Saturday night before your big date.

If you’re suffering from acne, here’s some practical advice:

• Think before you squeeze. Virtually all dermatologists will tell you to resist the urge to pop a zit. After all, the risks are legion—you might force the sebum deeper into your skin, worsen the inflammation, and cause scarring. However (and this is not the best topic among polite society), if you have a pimple that isn’t inflamed and is white, ripe, and raised above the surface of your skin, it’s safe to give it a tentative nudge. But if blood or clear liquid emerges, just walk away from the mirror before you do any damage.

• Try an over-the-counter lotion. Treat mild cases of acne with an overthecounter cream. The key ingredient to look for is benzoyl peroxide. There’s no magic formula, so don’t plunk down serious cash for the miracle cures shilled on late-night infomercials.

• Get help for acne that doesn’t improve. Don’t be an acne hero. Living with a bad case of acne can lead to scarring (and not just the psychological kind). Your friendly neighborhood dermatologist can prescribe an antibiotic lotion or an oral antibiotic that will change the balance of bacteria on your skin, ultimately reducing the inflammation.

Source of Information : Oreilly - Your Body Missing Manual