Did Depression Offer an Evolutionary Advantage?

A provocative new theory explores the possibility that depression is an evolutionary condition that protected our ancestors — from infection.

Such a theory could explain the ubiquity of depression which affects one in 10 adults in the United States. As such, experts believe the hypothesis that depression is “hard-wired” into our brains must be considered.

This has led biologists to propose several theories to account for how depression, or behaviors linked to it, can somehow offer an evolutionary advantage. Some proposals have focused on how depression influences behavior in a social context.

In a new article, a pair of psychiatrists addresses this puzzle in a different way, tying together depression and resistance to infection.

In this theory, researchers propose that genetic variations that promote depression also helped our ancestors fight infection. An outline of their proposal appears online in the journal Molecular Psychiatry.

Co-authors Andrew Miller, M.D., and Charles Raison, M.D., recognized that depression is often linked to inflammation or an overactivated immune system. People with depression tend to have higher levels of inflammation, even if they’re not fighting an infection.

“Most of the genetic variations that have been linked to depression turn out to affect the function of the immune system,” Miller said. “This led us to rethink why depression seems to stay embedded in the genome.”

“The basic idea is that depression and the genes that promote it were very adaptive for helping people — especially young children — not die of infection in the ancestral environment, even if those same behaviors are not helpful in our relationships with other people,” Raison said.

Until development of sulfa drugs and antibiotics in the early part of the 20th century, infection was a major cause of death. Surviving infection was a key determinant in whether someone was able to pass on his or her genes.

The authors propose that evolution and genetics have bound together depressive symptoms and physiological responses that were selected on the basis of reducing mortality from infection. Fever, fatigue/inactivity, social avoidance and anorexia can all be seen as adaptive behaviors in light of the need to contain infection, they write.

The theory provides a new explanation for why stress is a risk factor for depression. In theory, the stress-depression link is a side-product of a process that pre-activates the immune system in anticipation of injury.

Similarly, a disruption of sleep patterns can be seen in both mood disorders and when the immune system is activated. This may come from our ancestors’ need to stay on alert to fend off predators after injury, Miller said.

Experts believe the new theory could also guide future research on depression. A particular area of focus could be the use of inflammation biomarkers to help predict whether someone will respond to various treatments for depression.

Miller and Raison are involved in ongoing research on whether certain medications, which are normally used to treat autoimmune diseases, can be effective with treatment-resistant depression.

Natural Born Killers?

There's a glitch in the brain of violent criminals—but that doesn't mean they're insane. Is violent criminal behavior a mental disorder? A University of Southern California psychologist says yes--and he'll show you brain scans to back up his claim. Adrian Raine, Ph.D., led a team that compared brain activity in 22 murderers and 22 normal folks. Their tool of choice: the PET scan, an imaging technique that measures the brain's utilization of glucose, its primary fuel. The scans indicate which areas of the brain are active--and which are lying low. The researchers discovered that the prefrontal cortex, the brain region right behind the forehead, was less active in the murderers. Prefrontal deficiencies have been associated with a variety of behaviors--risk taking, rule breaking, aggression, and impulsivity--that can lead to violence. But there's a catch. The murderers in the study had all pleaded not guilty by reason of insanity. Might mental illness account for their abnormal PET scans? No, says Raine; insanity is a legal concept, not a medical condition. The variety of mental disorders the killers cited in their insanity pleas do not explain their lower prefrontal activity. If further studies confirm that murderers' brains are biologically different, does this mean that some of us are natural born killers? Not at all. Raine, who says his own brain scan resembles that of a man who killed 43 people, thinks that biological and environmental factors are both essential components of violent behavior. But the idea that killers' brains are different has profound implications for justice--and for rehabilitation. Cognitive remediation training has helped brain-injured patients recover lost function. If such therapy is able to help violent offenders beef up their brain to compensate for an underactive prefrontal cortex, the changes might show up on a PET scan. Come parole time, those scans could be far more convincing evidence of rehabilitation than a convict's professed remorse.

Surprising Results From One of The World’s Longest Longevity Studies

Surprising Results From One of The World’s Longest Longevity Studies

We’ve got surprising results from one of the world’s longest longevity studies. For the past 80 years a group of 1,500 people have had their lives, and their children’s lives combed through by researchers. The journey started when they were children in 1922, when a Stanford professor, named Lewis Terman, pulled them out of their classes and recruited them for his groundbreaking study. Terman followed his group, who became known as the “Termites,” until his death in the 1950’s but other scientists picked up right where he left off. Two of them are psychology professors Howard Freidman and Leslie Martin and they’ve just finished a book breaking down the most important findings in the study. They say their goal wasn’t just to find out how to live longer, it was how to live healthier too. Some of what they found is turning conventional wisdom on its head! Here are the top three surprising things Terman’s termites tell us about living a longer, healthier life:

* Stressed out worrywarts don’t always die young. Why? Because neurotic or conscientious people are less likely to get themselves into dangerous situations. They’re more likely to seek help when they have health issues and remember to take prescriptions. There’s more! Worriers may actually have different brain chemistry that makes them less susceptible to diseases!

* Job stress is also not going to force you into an early grave. The longevity researchers found that even when people don’t LOVE their jobs, the fact that they worked hard at them was a predictor of long life. That's because being productive and engaged indicates health and happiness.

* The final surprising finding: strenuous exercise doesn’t lead to a long life. The authors found that over the long term, doing things you really enjoy, like walking with friends or gardening, will help you stay healthier longer than running marathons.

Wandering Amnesia

A few years ago, Jeff Ingram, drove from his home in Olympia, Washington, to visit a terminally ill friend in Alberta. Four days later, he woke up on a street in Denver—without his car, his wallet, or any memory of who he was.

Ingram suffers from dissociative fugue—a rare form of amnesia in which people suddenly begin traveling (or continue, if on the road). They forget their identity, fail to recognize loved ones, and can't recall how they arrived wherever they are. Some later develop new personalities altogether. The trance lasts from a few hours to several years, and can involve travel across continents and oceans. One study put the average distance traveled by these wandering amnesiacs at 750 miles.

Whereas amnesia is typically precipitated by brain injury, those in fugue states are neurologically intact. Instead, the condition appears to be triggered by stress—often related to marital problems, financial worries, or depression. "They unconsciously run away from traumatic situations," says Philip Coons, professor emeritus at the Indiana University School of Medicine and an authority on the disorder. That's why the incidence of fugue rises during periods of war and natural disasters.

These wanderers sometimes turn to crime, such as vehicle theft and credit-card fraud. No one knows what they're thinking in-fugue, but it appears they live day-to-day with an emphasis on survival. Some have been found with stale bread and pockets full of jelly and ketchup packs. They become aware of their memory loss only after being asked questions about their lives. For Ingram, that occurred when he stumbled into a Denver hospital and was quizzed by the receptionist. He says he became scared and angry and wanted to know who he was.

Most sufferers eventually recover their pre-fugue memories—as suddenly as they lost them. Psychologists remain puzzled as to why. "One problem with trying to understand dissociative fugue is that by the time the patient comes to clinical attention, the fugue state is over," says psychologist Daniel Schachter, a memory expert at Harvard University. In cases where memory does not spontaneously return, therapists focus on resolving the underlying stress or trauma.

Even months after being reunited with his family, Ingram still has no pre-fugue memories. He's scared he might vanish again, so he's ordered a $400 pair of shoes loaded with GPS. "It's a small price to pay for the peace of mind," he says.

Case Study: Jeff Ingram—a former mill worker in Olympia, Washington

• Possible triggers: A friend's battle with cancer and the anniversary of 9/11.
• Spotted: His fiancee's brother recognized him when he appealed for help on TV news two months after his disappearance.
• Dejà vu: Ingram had disappeared once before. In 1995, while living in Alberta, he traveled more than 600 miles to Seattle, where he was discovered after nine months.
• Never again: In addition to ordering GPS shoes, Ingram has tattooed identifying information on his left arm and wears a zip disk with medical information around his neck.
• Happy ending: Although he cannot remember his three-year relationship with his fiancee pre-fugue, the two were married that December.

Your Guide to Better Sleep

From Journal Psychology Today:

It's what we do in response to a bout of insomnia that determines whether we will end up with long-term sleep problems. The fact is the sleep system tends to right itself after a few nights of insomnia—provided you make no adjustments to your sleep-wake cycle.

We all know that sleep is crucial to having the energy and ability to perform whatever it is we want to do. All it takes is one or two sleepless nights to drive home that point—and we all have a sleepless night or two sometimes. It's the cost of being human and having the capacity to worry about the future and chew over the past.

Yet, it's what we do in response to a bout of insomnia that determines whether we will end up with long-term sleep problems. The fact is that the sleep system tends to right itself after a few nights of insomnia—provided you make no adjustments to your sleep-wake cycle.

Unfortunately, most people take special measures to get some rest. They nap in the afternoon or evening. Or they go to bed early the next night, or sleep late the following morning. Or they take a drink or two to fall asleep.

Every one of these "corrective" measures interferes with your body's sleep "homeostat," a mechanism that builds up pressure for sleep and helps assure a good night's rest. The homeostatic pressure for sleep depends on how long you have been awake—and how active you are while awake.

I spoke to Dr. Michael Perlis, head of behavioral sleep medicine at the University of Rochester. An expert on insomnia, he has plenty of advice to offer on how to get the rest you need while steering clear of sleep problems.

• Get more exercise—physical and mental. It primes the sleep homeostat. It's a myth that exercise at bedtime is bad. Sex is, among other things, a great exercise.
  
  
• Set a regular bedtime—and keep it. Your body needs reliability.
  
  
• Set up conditions so that you catch the wave of sleep. Sleep has to be permitted. Take obstacles out of the way, and give up the notion that you can control sleep.
  
  
• Learn simple meditation and practice it before bedtime; it cuts down nervous system arousal.
  
  
• Put sleep in the background of your life. Don't monitor it, don't evaluate it.
  
  
• Jack up your body temperature with a warm bath before bed. Exaggerating the normal drop in body temperature that accompanies lying down abets sleep.
  
  
• Keep your bedroom dark, especially as you get older. Even small amounts of light and noise can disturb sleep as you age.
  
  
• Don't overheat your environment. Sleep loves cold. Keep your bedroom cold but load up on blankets.
  
  
• Less is more. The less you do in response to a bout of sleeplessness, the faster your sleep patterns will return to normal.
  
  
• Keeping your wake-up time constant but going to bed one hour later will help 25 percent of insomniacs in one to two weeks. Prepare to feel sleepy at times and avoid driving then. After two weeks, add back the time in half-hour increments.
  
  
• Look on two or three nights of insomnia as a gift—the gift of time you wanted to get done all that you have to get done. Insomnia may be functional, a signal that you need to attend to what got you up.
  
  
• Don't fight the insomnia. The homeostat makes sleep a self-reparative system—if you stay out of its way.
  
  
• Don't worry about the consequences of not sleeping. Worrying about insomnia can create insomnia.
  
  
• Don't sleep with your pets! Animal dander can create allergies that manifest only at night, and the movement of any pet on your bed can wake you up.
  
  
• Do not sleep later to make up for lost sleep. It de-primes the sleep homeostat and reduces pressure for sleep the next night, turning a night of sleeplessness into insomnia.
  
  
• Don't make up for a night of sleeplessness by napping. That undermines the sleep homeostat and makes it less likely you will sleep through the next night.
  
  
• Don't make up for an acute bout of insomnia by going to bed early.
  
  
• Do not try to induce sleepiness by drinking alcohol. Yes, it's a great relaxant—but it is metabolized so quickly it creates rebound insomnia within the night; it's so fast-acting you'll be up in four short hours.
  
  
• Limit caffeine to one cup of coffee in the morning. At age 18, caffeine has a half-life of 4.5 hours, which increases with age. Gradually eliminate caffeine altogether if you have trouble sleeping.

Perception of Time Can Increase Stress

By Selena Chavis:

In the driven U.S. social scene of full-time jobs, after-school children’s activities, volunteer obligations and just managing the day-to-day, many find that they are under increased stress.
Research conducted by a faculty member at New Jersey-based Rowan University suggests that the way people perceive time can either increase or decrease that stress.
Dr. Tejinder Billing, assistant professor of management in the Rohrer College of Business has studied the correlation between stress, time and work-family conflict in three different countries: the U.S., her native India and Venezuela.
Through her research, she has determined that while objective workload may represent a certain reality, the perception of that workload by an individual is more important.
“Individuals have a threshold level for workload, beyond which work is perceived as overload. When an individual’s workload exceeds the optimal level that he or she is comfortable with on a daily basis in the work situation, then psychological strain is the likely outcome,” she said
A silent variable in this equation of work and perception of work, according to Billing, is time.
“The essence of work overload is to do too much work in given amount of ‘time.’ Although we all continually refer to time, we quite easily forget about it when reflecting on stressful events,” she said.
Billings’ studies into time and workload commenced while she was studying at the University of Memphis and realized that people in the U.S. are “driven by the clock.”
“I actually didn’t find one single room in my school that didn’t have a clock. In India, clocks are not of such importance,” she noted, adding that cultural differences and attitudes toward time affect the way people manage time and deal with stress.
While Latin American and Asian cultures view time as an abundant resource, their Western counterparts are much more sensitive to the boundaries of time, Billings said, adding that people need to be aware of these differences when dealing with other cultures.
“If I’m not sensitive toward time like in Western countries, I can be in trouble when everyone is sensitive,” Billing said. “If I’m time-driven and you’re taking me to Latin America where perception of time is abundant, I’ll be stressed out.”
Billings said that people in the U.S. who put high emphasis on planning are better able to deal with work overload than those who do not emphasize planning and scheduling of activities in both their work and non-work lives.
In both the Indian and Venezuelan cultures, though, planning did not produce the same positive impact, which points to impact of perception of time across cultures.
Billings suggested that a key finding of the research is that people in the U.S. can manage and reduce stress more effectively by planning. “For individuals who emphasize planning and scheduling, the strength of the relationship between stressors and psychological strain is weaker than for individuals who do not emphasize planning and scheduling,” she said.
Research indicates that other factors influence our perception of time such as whether we were brought up to do things in sequential order or multi-task.
“We all have different attitudes toward time. We have different senses of time. And as a result we perceive and use time differently,” Billings noted.
One concept about time and perception rang true for all three cultures. Research revealed that people in the United States, India and Venezuela all feel stress when they perceive themselves as having too much work and too little time in which to get it done.
The differences are revealed in how they experience stress.

Birth Order and Personality

Experts tell NBC News that their place in the household is intertwined with everything - from their hobbies to their grades to how much money they’ll make as an adult. For example: The firstborn is used to being the center of attention because they had their parents all to themselves until a younger sibling came along. In fact, researchers say firstborns get 3,000 more hours of quality time with their parents than later-born kids. Firstborn children also tend to be overachievers, score higher on IQ tests, get more education, and are more likely to make six-figure salaries. However, all that success comes with a price. Firstborns tend to be inflexible, they don’t like change, and can be downright bossy because they’re given a lot of responsibility at home. They also have an intense fear of failure. So for some, nothing they accomplish feels good. Dr. Kevin Lerman is the author of “The Birth Order Book.” He says it’s important to let your firstborn know it’s okay if they don’t succeed at everything.

Next in the birth order: middle children. Middle kids go-with-the-flow and constantly negotiate and compromise in order to “fit in.” Since “mid-kids” get less attention at home and can feel left out, they form stronger bonds with friends. The fix: Occasionally put your middle child in the spotlight by letting them pick where to eat out or what movie to see, so that they get to feel in control of the family from time to time.

Finally, there’s the baby of the family. Experts say the baby generally isn’t the strongest or the smartest kid, but they find ways of getting attention. They’re natural charmers with an outgoing personality, and take a lot more physical risks when they play. Since their parents have already gone through older children learning to walk, talk, read and ride a bike, last-borns can feel that nothing they do is important. Experts say treat the youngest like they’re just as special as their siblings, and expect them to follow the same rules, too.

Why Handsome Men Make Bad Husbands

You may have recently heard or seen the news coverage (in the New York Daily News or CBS news online, among others; you may have even seen the lead author, James K. McNulty of the University of Tennessee, discuss it on the Today show) of a study, published in the Journal of Family Psychology, that showed that couples in which the woman is physically more attractive than the man are happier than couples in which the man is physically more attractive than the woman. Why is this? Why is it better for the couple if the woman is physically more attractive than the man?
If you have been keeping score at home, the findings of this study should have come as no surprise to you. There are two different reasons why couples in which the woman is more attractive than the man are more successful and happier than couples in which the man is more attractive than the woman.
First, as we elaborate in Chapter 4 of our book Why Beautiful People Have More Daughters (“Go Together Like a Horse and Carriage? The Evolutionary Psychology of Marriage”), handsome men on average make bad husbands. Men can maximize their reproductive success by pursuing one of two different strategies: Seek a long-term mate, stay with her, and invest in their joint offspring (the “dad” strategy); or seek a large number of short-term mates without investing in any of the resulting offspring (the “cad” strategy).
All men may want to pursue the cad strategy; however, their choice of the mating strategy is constrained by female choice. Men do not get to decide with whom to have sex; women do. And women disproportionately seek out handsome men for their short-term mates for their good genes. Even women who are already married benefit from short-term mating with handsome men if they could successfully fool their husbands into investing in the resulting offspring. The women then get the best of both worlds: Their children carry the high-quality genes of their handsome lover and receive the parental investment of their unknowingly cuckolded but resourceful husband. (In order to help the women accomplish this, evolution has designed women to be more likely to have sex with their lovers when they are ovulating and therefore fertile, and have sex with their husbands when they are not.)
Thus, handsome men get a disproportionate number of opportunities for short-term mating and are therefore able to engage in the cad strategy. Ugly men have no choice. Since women do not choose them as short-term mates, their only option for achieving any reproductive success is to find one long-term mate and invest heavily in their children -- the dad strategy.
Consistent with this logic, studies show that more attractive men have a larger number of extra-pair sex partners (sex partners other than their long-term mates). Interestingly, more attractive men have more short-term mates than long-term mates, whereas more attractive women have more long-term mates than short-term mates. Most importantly for our current purposes, handsome men invest less in their exclusive relationships than ugly men do. They are less honest with and less attentive to their partners. McNulty’s new study of newlyweds confirms this. Their data show that the more physically attractive the husbands are, the less supportive they are of their wives in their interactions.
I hasten to add that “good” and “bad” (as in the title of this post “Why handsome men make bad husbands”) are value judgments that scientists do not make. However, empirical data do demonstrate clearly that handsome men have more extra-marital affairs and are not as committed to their marriages, which many wives would undoubtedly consider undesirable. In this sense, handsome men make better lovers than husbands.

Study: Alcohol Tied to Nearly 1 in 25 Deaths

Alcohol May Be Related to 3.8% of Global Deaths, New Study Estimates

June 25, 2009 -- Approximately 4% of global deaths may be linked to alcohol, according to a new study.
The study, published in The Lancet, estimates the percentage of alcohol-related deaths based on accidents, alcohol abuse, and various health conditions -- including certain cancers, high blood pressure, and liver problems -- in which alcohol may play a role.
The researchers -- who included Jurgen Rehm, PhD, of the Centre for Addiction and Mental Health in Toronto -- analyzed 2003 data from the World Health Organization (WHO), the United Nations, and other sources.
When Rehm and colleagues calculated their estimates, they considered the health risks and benefits of alcohol, as well as alcohol consumption patterns, with the highest rate of alcohol consumption in Eastern Europe and Russia and the lowest rate in the eastern Mediterranean region, which mainly includes countries in the Middle East and northern Africa.
Rehm's team notes that alcohol-related deaths were most common in men and young adults, and that alcohol consumption is rising among women and in India and China.

All About Acai Berry

From HealthCastle:
Acai berry has recently been featured on many high-profile talk shows, and a quick Google search returns multiple websites promoting some form of it. If you are curious about all the hype, read on for the lowdown on this fruit.

What is Acai Berry?

Not many fruits have as alluring a name as Acai berry. Acai (pronounced ah-sah-EE) berry is the fruit of the Acai palm, one of many species of palms belonging to the genus Euterpe, which is native to Central and South America. The palm is fast-growing, and both the fruits and the hearts of the palm are important food sources for locals. The berry's growing popularity in North America has led to multiple brands of Acai berry supplements (alone or mixed with other fruit juices) offered in the market. Health claims on these products include weight loss, detoxifying, wrinkle-fighting, higher energy levels and superior levels of antioxidants.

What Acai Berry Research Shows

Several studies have been done on the antioxidant activity of the juice or fruit pulp (including a freeze-dried form of supplement). Generally, they agree that Acai berry exhibits some antioxidant activity but, depending on the methods used to define "antioxidant activity," the conclusions about the Acai berry's specific potency vary. A 2006 Brazilian study of the antioxidant activity of the pulp of various fruits commonly consumed in Brazil showed that Acai berry pulp had less antioxidant activity than acerola, mango, strawberry, and grapes, but more antioxidant activity than guava, passionfruit, and pineapple. A 2008 study in the Journal of Agricultural and Food Chemistry (funded by a pomegranate juice maker) used four different methods of testing antioxidant activity in fruit juices and showed that Acai berry juice had less antioxidant activity than red wine, pomegranate juice, Concord grape juice, and blueberry juice, equivalent activity to black cherry and cranberry juices, and more antioxidant activity than orange or apple juices. Note that most of the studies so far focus on the antioxidant capacity as determined by chemical analysis/assays; these tests do not guarantee that the antioxidants would behave the same way inside our bodies.

A couple of studies in the same journal fed Acai berry juice to 12 healthy volunteers and documented higher levels of antioxidants in the blood for up to two hours after consumption, but again, there is no clear health benefit that can be drawn from this observation. It is also unclear what form or forms of Acai berry would be optimally absorbed by our bodies.

The Bottom Line

Like many other fruits, Acai berry contains antioxidants. There is currently no clear evidence of any superiority in the action of Acai berry's antioxidants when compared to other types of fruits. Try it if you're curious, but at times like these when everyone is watching their food budget, your hard-earned dollars are probably better spent buying a great variety of fresh produce, whether fruits or vegetables.

Is Sugar Like a Drug?

From Shereen Jegtvig:

Research presented at the annual meeting of the American College of Neuropsychopharmacology shows how rats respond to sugar binges just like they would respond to morphine, cocaine or nicotine.

"Our findings with lab rats show that intermittent access to sugar can lead to changes in the brain and behavior similar to those caused by drugs of abuse," said Bart Hoebel, PhD, Professor of Psychology, Princeton University. "In certain models, sugar-bingeing causes long-lasting effects on the brain and increases the inclination to take other drugs of abuse, including alcohol."

Hungry rats were fed sugar water and researchers discovered that the rats' brains released neurotransmitters called dopamines thought to be involved in addiction. Further tests elicited withdrawal symptoms in the same rats.

Interesting research.

I don't usually write much about diet and nutrition studies with rats and other non-human animals because they don't always translate well to human behavior. We still don't really know for sure that sugar is chemically addicting or if there are emotional issues involved with eating too many sweets and suffering from sugar cravings that rats probably don't experience. However, we know there are connections between sugar craving and having low serotonin levels. One thing I find interesting, though, is that the rats in the study were deprived of food for twelve hours before being fed sugar water, so I'm not sure how much of the dopamine response was just from relief of hunger (though the researchers say this shouldn't happen with other foods that apparently are boring to rats) or directly due to sugar. In either case, it suggests possible addictive brain chemistry.

So, since you're not a rat, how does research like this affect you? Now that we're deep into the holiday season, you may have lots of parties to attend with lots of sumptuous foods and decadent desserts. Don't starve yourself all day 'saving up' your calories for the party foods -- it may be bad for your brain and you might go off the sugar-bingeing deep end. Instead, eat normally and choose healthy foods throughout the day with lots of nutrients and fiber (like fruits and vegetables). Then later, when you are faced with all those delicious holiday treats, it may actually be easier to control your cravings.

Losing a Little Sleep Affects More Than Attention Span

SLEEP RESEARCH
By Rob Stein
Washington Post Staff Writer
Sunday, October 9, 2005; A01

With a good night's rest increasingly losing out to the Internet, e-mail, late-night cable and other distractions of modern life, a growing body of scientific evidence suggests that too little or erratic sleep may be taking an unappreciated toll on Americans' health.

Beyond leaving people bleary-eyed, clutching a Starbucks cup and dozing off at afternoon meetings, failing to get enough sleep or sleeping at odd hours heightens the risk for a variety of major illnesses, including cancer, heart disease, diabetes and obesity, recent studies indicate.

"We're shifting to a 24-hour-a-day, seven-day-a-week society, and as a result we're increasingly not sleeping like we used to," said Najib T. Ayas of the University of British Columbia. "We're really only now starting to understand how that is affecting health, and it appears to be significant."

A large, new study, for example, provides the latest in a flurry of evidence suggesting that the nation's obesity epidemic is being driven, at least in part, by a corresponding decrease in the average number of hours that Americans are sleeping, possibly by disrupting hormones that regulate appetite. The analysis of a nationally representative sample of nearly 10,000 adults found that those between the ages of 32 and 49 who sleep less than seven hours a night are significantly more likely to be obese.

The study follows a series of others that have found similar associations with other illnesses, including several reports from the Harvard-run Nurses' Health Study that has linked insufficient or irregular sleep to increased risk for colon cancer, breast cancer, heart disease and diabetes. Other research groups scattered around the country have subsequently found clues that might explain the associations, indications that sleep disruption affects crucial hormones and proteins that play roles in these diseases.

"There has been an avalanche of studies in this area. It's moving very rapidly," said Emmanuel Mignot of Stanford University, who wrote an editorial accompanying the new obesity study in the October issue of the journal Sleep. "People are starting to believe that there is an important relationship between short sleep and all sorts of health problems."

Not everyone agrees, with some experts arguing that any link between sleep patterns and health problems appears weak at best and could easily be explained by other factors.

"There are Chicken Little people running around saying that the sky is falling because people are not sleeping enough," said Daniel F. Kripke of the University of California at San Diego. "But everyone knows that people are getting healthier. Life expectancy has been increasing, and people are healthier today than they were generations ago."

Other researchers acknowledge that much more research is needed to prove that the apparent associations are real, and to fully understand how sleep disturbances may affect health. But they argue that the case is rapidly getting stronger that sleep is an important factor in many of the biggest killers.

"We have in our society this idea that you can just get by without sleep or manipulate when you sleep without any consequences," said Lawrence Epstein, president of the American Academy of Sleep Medicine. "What we're finding is that's just not true."

While many aspects of sleep remain a mystery -- including exactly why we sleep -- the picture that appears to be emerging is that not sleeping enough or being awake in the wee hours runs counter to the body's internal clock, throwing a host of basic bodily functions out of sync.

"Lack of sleep disrupts every physiologic function in the body," said Eve Van Cauter of the University of Chicago. "We have nothing in our biology that allows us to adapt to this behavior."

The amount of necessary sleep varies from person to person, with some breezing through their days on just a few hours' slumber and others barely functioning without a full 10 hours, experts say. But most people apparently need between about seven and nine hours, with studies indicating that an increased risk for disease starts to kick in when people get less than six or seven, experts say.

Scientists have long known that sleep disorders, such as sleep apnea, narcolepsy and chronic insomnia, can lead to serious health problems, and that difficulty sleeping may be a red flag for a serious illness. But the first clues that otherwise healthy people who do not get enough sleep or who shift their sleep schedules because of work, family or lifestyle may be endangering their health emerged from large epidemiological studies that found people who slept the least appeared to be significantly more likely to die.

"The strongest evidence out there right now is for the risk of overall mortality, but we also see the association for a number of specific causes," said Sanjay R. Patel of Harvard Medical School, who led one of the studies, involving more than 82,000 nurses, that found an increased risk of death among those who slept less than six hours a night. "Now we're starting to get insights into what's happening in the body when you don't get enough sleep."

Physiologic studies suggest that a sleep deficit may put the body into a state of high alert, increasing the production of stress hormones and driving up blood pressure, a major risk factor for heart attacks and strokes. Moreover, people who are sleep-deprived have elevated levels of substances in the blood that indicate a heightened state of inflammation in the body, which has also recently emerged as a major risk factor for heart disease, stroke, cancer and diabetes.

"Based on our findings, we believe that if you lose sleep that your body needs, then you produce these inflammatory markers that on a chronic basis can create low-grade inflammation and predispose you to cardiovascular events and a shorter life span," said Alexandros N. Vgontzas of Pennsylvania State University, who recently presented data at a scientific meeting indicating that naps can help counter harmful effects of sleep loss.

Other studies have found that sleep influences the functioning of the lining inside blood vessels, which could explain why people are most prone to heart attacks and strokes during early morning hours.

"We've really only scratched the surface when it comes to understanding what's going on regarding sleep and heart disease," said Virend Somers of the Mayo Clinic in Rochester, Minn. "I suspect as we understand more about this relationship, we'll realize how important it really is."

After several studies found that people who work at night appear unusually prone to breast and colon cancer, researchers investigating the possible explanation for this association found exposure to light at night reduces levels of the hormone melatonin. Melatonin is believed to protect against cancer by affecting levels of other hormones, such as estrogen.

"Melatonin can prevent tumor cells from growing -- it's cancer-protective," said Eva S. Schernhammer of Harvard Medical School, who has conducted a series of studies on volunteers in sleep laboratories. "The theory is, if you are exposed to light at night, on average you will produce less melatonin, increasing your cancer risk."

Other researchers are exploring a possible link to other malignancies, including prostate cancer.

"There's absolutely no reason it should be limited to breast cancer, and it wouldn't necessarily be restricted to people who work night shifts. People with disrupted sleep or people who are up late at night or get up frequently in the night could potentially have the same sort of effect," said Scott Davis of the University of Washington.

The newest study on obesity, from Columbia University, is just the latest to find that adults who sleep the least appear to be the most likely to gain weight and to become obese.

Other researchers have found that even mild sleep deprivation quickly disrupts normal levels of the recently discovered hormones ghrelin and leptin, which regulate appetite. That fits with the theory that humans may be genetically wired to be awake at night only when they need to be searching for food or fending off danger -- circumstances when they would need to eat to have enough energy.

"The modern equivalence to that situation today may unfortunately be often just a few steps to the refrigerator next door," Mignot wrote in his editorial.

In addition, studies show sleep-deprived people tend to develop problems regulating their blood sugar, which may put them at increased risk for diabetes.

"The research in this area is really just in its infancy," Van Cauter said. "This is really just the tip of the iceberg that has just begun to emerge."

© 2005 The Washington Post Company