Chapter 14. Biological Rhythms, Sleep, and Dreaming
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By Janet Raloff Psychiatrists sometimes prescribe light therapy to treat a form of depression in people who get too little morning sun. But too much light at other times may actually trigger such mood disorders. Chronic exposure to light at night unleashes depression, a new study finds — at least in animals. The new data confirm observations from studies of people who work night shifts, says Richard Stevens of the University of Connecticut Health Center in Farmington. Mood disorders join a growing list of problems — including cancer, obesity and diabetes — that can occur when light throws life out of balance by disrupting the biological clock and its timing of daily rhythms. In the new study, appearing online July 24 in Molecular Psychiatry, Tracy Bedrosian, Zachary Weil and Randy Nelson of Ohio State University exposed Siberian hamsters to normal light and dark cycles for four weeks. For the next four weeks, half of the animals remained on this schedule, and the rest received chronic dim light throughout their night. Compared with animals exposed to normal nighttime darkness, those getting dim light at night lost their intense preference for sweet drinks, “a sign they no longer get pleasure out of activities they once enjoyed,” Bedrosian says. In a second test, animals were clocked on how long they actively tried to escape a pool of water. Hamsters exposed to night lights stopped struggling and just floated in the water — a sign of “behavioral despair” — 10 times as long as animals that had experienced normal nighttime darkness, Bedrosian reports. © Society for Science & the Public 2000 - 2012
Analysis by Emily Sohn Have a birthday in September, October, or November? Lucky you. You may have above-average chances of living an extra-long life. In a recent study, researchers from the University of Chicago looked at data from more than 1,500 people who were born between 1880 and 1895 and who lived to be 100 or older. The researchers compared that data with the birth months and life spans of nearly 12,000 of the centenarians’ siblings and spouses. The majority of people who lived an extra-long life were born between September and November, the researchers reported in the Journal of Aging Research http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3236478/. Birthdays in March, May, and July produced 40 percent fewer centenarians. The findings support a growing body of evidence that the conditions we experience extremely early in life may influence our health and survival many decades later, the researchers say. By comparing centenarians to their siblings, the study aimed to take into account living conditions early in life. By comparing spouses, the idea was to consider living conditions later in life. The study didn’t offer a definitive explanation for the birth and death patterns, though the researchers offered some theories. It’s possible, for example, that pregnant mothers had access to different levels of nutrition at different times of year in the late 1800s. Seasonal rates of infection may have also influenced fetuses in the womb, with vulnerability peaking during certain developmental periods. © 2012 Discovery Communications, LLC.
By ANAHAD O'CONNOR For Lisa Hanson, a stay-at-home mother in San Francisco, the alarm that used to rouse her out of sleep most mornings was the sound of her toddler. “He wakes up at 5:30 screaming sometimes,” she said. “It would jolt me awake, and then I’d be miserable and groggy all morning because I’d be woken up when I’m in my deepest sleep.” But last month, Ms. Hanson started using a new program, the Renew SleepClock, an iPhone app that keeps track of her sleep. Its makers, GEAR4, say that the app uses radio sensors to detect breathing patterns and movements at night, then uses that information to wake a person at the lightest point of sleep, the optimal time to wake up. The theory is that awaking from light sleep, as opposed to the deep stages of sleep, helps reduce so-called sleep inertia, the cloud of grogginess and impaired alertness that makes people desperately want to crawl back into bed. The app also acts as a sort of sleep adviser, giving Ms. Hanson guidance about the amount of shut-eye to shoot for and ways to get there. “Since I’ve been using it, I do feel better,” Ms. Hanson said. “It’s waking me up in a more ideal stage of sleep and helping me have that much better of a day.” The Renew SleepClock, which costs $199, is the latest addition to a new generation of smartphone apps designed to analyze and improve sleep patterns. While experts have warned for years that gadgets like smartphones are increasingly disrupting sleep by keeping us connected 24/7, these programs claim to do the opposite. Two other products that have gained followings are the WakeMate ($59.99), a wristband worn at night that wirelessly transmits data to the user’s smartphone, and the Zeo Sleep Manager-Mobile ($99), which uses a sensor-equipped headband to collect data about the user’s sleep habits. Copyright 2012 The New York Times Company
Link ID: 17022 - Posted: 07.11.2012
By Morgen E. Peck Anyone who has pulled an all-nighter knows it is possible to be tired without being sleepy. The body slows and concentration slips, even as thoughts spin toward a manic blur. It feels as though the sleep-deprived brain is actually becoming more active. And indeed it is, according to a recent study in the journal Cerebral Cortex. Marcello Massimini, a neurophysiologist at the University of Milan in Italy, found that the brain becomes more sensitive as the day wears on. The experiment, he explains, is like poking a friend in the ribs to see how high he jumps. Massimini prodded brain cells in the frontal cortex with a jolt of electricity, delivered via noninvasive transcranial magnetic stimulation. Then he observed how the rest of the brain responded, comparing results from subjects who had been awake for two, eight, 12 or 32 hours. “I'm sure if you bump your friend when he's sleep-deprived, he's going to jump higher,” he says. The sleep-deprived brain, it turns out, also gets jumpy, responding to the electrical jolt with stronger, more immediate spikes of activity. The results jibe with a widely held theory that while we are awake, our neurons are constantly forming new synapses, or connections to other neurons, which ramps up the activity in our brain. Many of these connections are irrelevant, but the only way to prune them is by shutting down for a while. The theory explains why it is difficult to cram new information into a sleepy brain. But it also helps to explain some unusual medical observations: epileptics are more likely to have seizures the longer they stay awake, and severely depressed patients with abnormally low brain activity sometimes improve after skipping sleep. “You keep them awake for one night, and, incredibly, they get better,” Massimini says. © 2012 Scientific American,
By Laura Sanders A dreamland ditty played softly during a nap helps people hit the right notes while awake. Soft tones during sleep creep into the napping brain and strengthen playing skills, researchers report online June 24 in Nature Neuroscience. The results don’t mean that after a nighttime Beethoven sonata, a piano novice will wake up with the ability to play it. But the results do suggest that an existing skill can be sharpened during a nap, says study coauthor Ken Paller of Northwestern University in Evanston, Ill. Earlier work by Paller and others has found that sound and odor cues during sleep can improve a person’s memory for the locations of objects. The new study extends those results by showing that a learned skill — in this instance, playing music — can also be influenced during sleep. Although these sorts of experiments are just getting started, “the door is wide open,” Paller says. Musical ability, athletic prowess and other talents that normally require a lot of practice may be amenable to boosts during sleep. Before the easy job of having a nap, 16 right-handed participants in the study had to do some actual work. Volunteers learned two different not-very-catchy tunes, played with their left hands on the a, s, d and f keys of a computer. In an arrangement similar to that of Guitar Hero, circles that floated up the screen told participants which key to hit and when. © Society for Science & the Public 2000 - 2012
By Susan Carnell One of the strangest findings to emerge from the world of obesity science lately is that people who sleep less tend to weigh more. But until recently, we have been stifling our yawns and scratching our heads about why: Does lack of sleep alter our biology? Or does it affect our eating behavior? Now two brain-imaging reports suggest the answer is both. The first study, published in March in the Journal of Clinical Endocrinology & Metabolism, looked at the effects of one night of no sleep. The second, published in April in the American Journal of Clinical Nutrition, tested the impact of nearly a week of more commonly experienced levels of sleep deprivation (four hours of sleep for six nights). Both studies used functional MRI to measure brain activation as their subjects viewed food pictures—analogous to being bombarded with a stream of McMuffin ads after a long night of working (or partying). Each study discovered that sleep loss caused areas within a key motivation network, including the striatum and anterior cingulate cortex, to go into overdrive at the mere sight of food. The same circuit perks up when addicts view images of their substance of choice. “Calories are energy, and your brain subconsciously knows they will wake you up,” says Marie-Pierre St-Onge of Columbia University, lead investigator of the April study. She likens the superresponsive sleep-poor brain to that of someone who has lost weight on a drastic diet—devouring the first snack you can get your hands on is a “no-brainer.” © 2012 Scientific American
By Ferris Jabr In the 18th century Carl Linnaeus named them lemurs, after the Latin lemures—spirits of the dead, wandering ghosts. He knew the primates roamed Madagascar’s forests at night, their large eyes brimming with moonlight, their shrill cries crashing through the treetops. One of the smallest lemurs on the island, the fat-tailed dwarf lemur, resembled a phantom in another way: it completely vanished for seven months each year. For a long time, no one understood where the fat-tailed dwarf lemur went—a remote part of the island? the spirit world?—or what it was doing all that time, but scientists had a hunch. Perhaps the lemur was hibernating. If so, it would be the only primate in the world—and one of the only tropical mammals—to do so. Given Madagascar’s climate, however, it made sense that a lemur might hibernate to survive annual periods of drought. In general, Madagascar has two seasons: the hot, wet season from November to April, and the cooler, dry season from April through October. The deciduous forests on the west coast, where many fat-tailed dwarf lemurs live, offer no open sources of water during the dry season and only fibrous fruits bereft of sugar. Perhaps, scientists reasoned, the fat-tailed dwarf lemur hunkered down and waited for the rains to return, slowing its metabolism and dropping its body temperature. It could survive off of nutrients stored in its tail, which always grew plumper as the dry season drew closer. © 2012 Scientific American
Link ID: 16939 - Posted: 06.20.2012
By Charles Q. Choi Sleep should be the great equalizer. Whatever differences might divide us during the day, the nonconsciousness that comes with nighttime should be one thing we all have in common. It ain't necessarily so. Scientists have now found significant differences exist in how people sleep in the U.S. depending on race, ethnicity and country of origin, suggesting genetic or cultural differences in shut-eye patterns. This line of research could help identify how these disparities might affect health and find better ways to improve sleep. One study looked at sleep data gathered from more than 430,000 people in the U.S. between 2004 and 2010 as part of the National Health Interview Surveys, which the U.S. Centers for Disease Control and Prevention conducts annually to monitor the country's well-being. They found that foreign-born respondents were generally more likely to sleep the recommended healthy six to eight hours each night as compared with native-born Americans. "This study is particularly interesting, because it goes to show that the unhealthy American lifestyle includes more than a poor diet and lack of exercise—it also means unhealthy sleep patterns, and this can lead to important health consequences," says sleep researcher Michael Grandner at the University of Pennsylvania, who did not take part in this research. "It seems like foreign-born Americans may be protected by not adopting this unhealthy lifestyle." © 2012 Scientific American
Link ID: 16935 - Posted: 06.20.2012
By Brian Alexander A CPAP device, the Darth Vader-like mask used to ease breathing in sleep apnea sufferers, might be the least attractive thing a man can wear at night, but it could wind up improving his sex life, according to a new study released today at an annual meeting of sleep experts. In yet another example of how the human penis can serve as an important health indicator, a team of doctors from the Sleep Disorders Center of the Walter Reed National Military Medical Center has found that erectile dysfunction is common in younger men with sleep apnea, but that E.D. -- and libido -- improves in men who use the CPAP, or continuous positive airway pressure machine. They presented their results today at the meeting of the Associated Professional Sleep Societies in Boston. Over the past few years, medical science has repeatedly shown that how a man’s penis is working can reflect how the rest of his body is working. E.D. can be an early sign of diabetes, cardiovascular disease, high blood pressure and poor fitness, among other ailments. So when army captain Dr. Joseph Dombrowsky looked at a small handful of studies that had linked apnea to E.D., he realized that he had access to a pool of possible test subjects -- military beneficiaries newly diagnosed with the sleep disorder -- that he could use to explore the link. Dombrowsky and his colleagues recruited 92 men with an average age of nearly 46 who had both a new diagnosis of obstructive sleep apnea, or OSA, and who were starting therapy with CPAP machines. © 2012 msnbc.com
By JoNel Aleccia Attention, busy middle-aged folks. You may be healthy and thin, but if you habitually sleep less than six hours a night, you still could be boosting your risk of a stroke. That’s the surprising conclusion of a new study being presented Monday at SLEEP 2012, the annual meeting of the nation’s sleep experts. Getting too little shut-eye appeared to more than quadruple the risk of stroke symptoms among healthy, normal-weight people aged 45 and older, according to a study of some 5,600 people followed for up to three years. “The really important take-home message is this: Don’t blow it off. Sleep is just as important as diet and exercise,” said Megan Ruiter, the University of Alabama at Birmingham researcher who led the study. Experts recommend that healthy adults get between seven and nine hours of sleep a night. But about one in three U.S. workers regularly gets less than seven hours of snooze time, according to a recent government health report. Ruiter and her colleagues reviewed data from some 30,239 people participating in the REGARDS study – Reasons for Geographic and Racial Differences in Stroke – sponsored by the National Institutes of Health. Of those, they teased out some 5,666 people who were healthy at the start of the study – no history of stroke, stroke symptoms, so-called “mini-stroke” or transient ischemic attack, or elevated risk for sleep apnea and other sleep-disordered breathing problems. © 2012 msnbc.com
Content provided by Jennifer Welsh, LiveScience Night owls often wake up for work or school with a scowl on their faces and wishing for an IV drip of coffee, while morning people come skipping in 15 minutes early. However, morning people aren't chipper just as the sun is coming up; they are happier and more satisfied with life overall, a new study suggests. Teenagers' night owl tendencies fade as they age, and the study says this switch to a morning-focused schedule could be why older adults are happier than younger ones. "Past research has suggested that morning-type people report feeling happier than evening-type people, and this research was only on young adults," study researcher Renee Biss, a graduate student at the University of Toronto, told LiveScience. The new study looked across the lifespan to see if the morning habits of older individuals contributed to their overall life outlook. The researchers studied two populations: a group of 435 adults ages 17 to 38, and a group of 297 older adults, ages 59 to 79. Both groups filled out questionnaires about their emotional state, how healthy they feel and their preferred "time of day." [Life's Extremes: Early Birds vs. Night Owls] By age 60, most people are morning types, the researchers found. Only about 7 percent of young adults are morning larks, but as the population ages, this switches — in the older years only about 7 percent of the population are still night owls. © 2012 Discovery Communications, LLC.
By Scicurious Most of us will suffer sleep deprivation at one time or another. I’m not talking our usual state of broken sleep, 5 hours a night, or something else. I’m talking a full night without sleep, the kind many people experience in the army, with a brand new (or not so brand new) baby, or more frivolously (I hope), in college. We all know what sleep deprivation does to us. We’re unable to pay attention. We’re often cold or hot. We can’t think straight, we start doing very strange things (you would not BELIEVE the crazy dances I’ve made up…), and of course, we’re really, really tired. But why do these symptoms happen? What’s going on in the brain during sleep deprivation to explain this behavior? Well, in part, it might be changes in your D2 receptors. There are lots of signs that point toward the involvement of the neurotransmitter dopamine in wakefulness. Drugs that increase levels of dopamine in brain (including, but not limited to, drugs like cocaine, amphetamine, meth, and Ritalin) also increase feelings of wakefulness. Increasing dopamine in the brain via genetic alterations, like getting rid of the dopamine transporter in a mouse, stopping dopamine from getting recycled, produces a mouse that sleeps less. Diseases that are characterized by low dopamine levels, like Parkinsons, also have daytime sleepiness. But a neurotransmitter is only as good as its receptor. Dopamine has two main types of receptors, and the current hypothesis is that the wakefulness promoting effects of dopamine may be controlled partially by the D2 type receptor. Antipsychotics, which block D2 type receptors, make people sleepy, and previous studies showed decreased D2 binding in the brains of sleep deprived people. © 2012 Scientific American
By Tina Hesman Saey WASHINGTON — A protein famous for slowing aging and increasing life span also acts as a metronome, helping coordinate metabolism and the body’s daily rhythms. SIRT1, one of a group of proteins called sirtuins, plays roles in many cellular processes, including aging. Researchers hope that activating the protein with drugs such as resveratrol can extend life span and improve health for people, as it does in animal studies. Now, researchers at MIT have evidence that SIRT1 may not only help determine long-term health and longevity, but it also has a hand in setting the body’s daily or “circadian” clock. The finding, reported May 31 at the Metabolism, Diet and Disease meeting, could be important for understanding how metabolism and life span are linked. Studies of cells in laboratory dishes had suggested that SIRT1 might work with certain gears of the circadian clock in liver cells. But until now no one has shown that the protein could influence the body’s master clock in the brain, says Raul Mostoslavsky, a molecular biologist at Harvard Medical School. In the new study, scientists led by Leonard Guarente of MIT monitored the natural activity patterns of mice. Normally, mice’s circadian clocks run just shy of a 24-hour day, at about 23.5 hours. Mice that lack SIRT1 in their brains have a longer internal day, closer to 24 hours, Guarente said. And mice that made twice as much SIRT1 as normal in their brains had a shorter-than-usual day. Mice making five times as much SIRT1 as normal had even shorter natural days. © Society for Science & the Public 2000 - 2012
By Bora Zivkovic The biannual meeting of the Society for Research on Biological Rhythms happened last week. Unfortunately, I could not attend, so will have to wait another two years for the next opportunity. I am not sure how this stuff happens, but there was a flurry of new papers in the circadian field just preceding the event. Several of them have already received quite a lot of attention in both old and new media, and rightfully so, but I decided not to cover them one at a time just as the embargo lifted for each one of them. Instead, I will just very briefly describe and explain the main take-home messages of each one of them, link to the best coverage for those who want more detail (“Cover what you do best. Link to the rest.“), and then try to come up with more of a ‘big picture’ summary of the current state of the field. I apologize in advance for covering and linking to some of the papers that are not published in Open Access journals. I am not as strict about this policy as some other bloggers are (“if my readers cannot access it, they cannot fact-check me”), and will occasionally cover non-OA papers. Even if most of my readers cannot access them, I gather that a miniscule proportion can access and, if I got something wrong, can alert the other readers in the comments. And speaking of Open Access, I am not one to sign many online petitions, but this one is worth it so please sign if you have not done it already. So, let’s see what new and exciting in chronobiology these days… © 2012 Scientific American,
By Meghan Holohan You're drifting off to sleep, when suddenly you feel like you're plunging off a cliff -- and you jerk awake. The jolt is disorienting, and you must try again to fall asleep. As many as 70 percent of people experience sleep starts or hypnic jerks while falling asleep, says Dr. William Kohler, medical director of the Florida Sleep Institute and director of the pediatric sleep services at Florida Hospital, Tampa. “A hypnic jerk or sleep starts are a perfectly normal occurrence that is almost universal,” explains James K. Walsh, executive director and senior scientist at St. Luke’s Sleep Medicine and Research Center in St. Louis. “It involves a total body experience where your muscle contracts therefore your limbs jerk or your body twitches. They generally occur during the transition between wakefulness and sleep. All of these things are very, very brief, lasting a half second or less.” Hypnic jerks are myoclonus twitches, or involuntary muscle spasms, but sleep starts occur during hypnagogia, the stage when the body is falling asleep. While most people have felt hypnic jerks, a small number of people experience the frightfully-named exploding head syndrome, the sensation that there is an explosion, crashing cymbals, or thunder near (or in) one’s head. Exploding head syndrome is so rare that it is mostly reported by individual case studies. While exploding head syndrome distresses people with it, both Walsh and Kohler stress that this, too, is normal and not a sign of any problem, physical or mental. © 2012 msnbc.com
Link ID: 16830 - Posted: 05.23.2012
By Susan Milius Throughout the world, climate change is causing age-old ecological partners to miss their cues as seasons shift. The trend may be so strong at higher latitudes that researchers now propose that some species’ ranges could actually shrink away from the poles. This idea comes from studying broad-tailed hummingbirds that migrate north from Central America each spring to high-altitude breeding sites in the western United States. With only brief mountain summers to raise chicks, male hummingbirds typically arrive in the region before the first flowers bloom and scout for territories. Around the Rocky Mountain Biological Laboratory in Gothic, Colo., near the upper limit of the broad-tailed hummingbird breeding range, the gap between the first hummingbird arrival and the first bloom has narrowed by roughly 13 days during the last four decades. Amy McKinney of the University of Maryland in College Park and her colleagues report the discovery online May 14 in Ecology. Glacier lilies start blooming roughly 17 days earlier than they did in the 1970s, but birds haven’t sped up nearly as much. In a few extreme years, lilies have already started blooming before the first hummingbird showed up. Researchers calculate that if the timing trends continue, in about two more decades the males will routinely miss the first flowers. © Society for Science & the Public 2000 - 2012
By ANAHAD O'CONNOR Two new studies have found that people with sleep apnea, a common disorder that causes snoring, fatigue and dangerous pauses in breathing at night, have a higher risk of cancer. The new research marks the first time that sleep apnea has been linked to cancer in humans. About 28 million Americans have some form of sleep apnea, though many cases go undiagnosed. For sleep doctors, the condition is a top concern because it deprives the body of oxygen at night and often coincides with cardiovascular disease, obesity and diabetes. “This is really big news,” said Dr. Joseph Golish, a professor of sleep medicine with the MetroHealth System in Cleveland who was not involved in the research. “It’s the first time this has been shown, and it looks like a very solid association,” he said. Dr. Golish, the former chief of sleep medicine at the Cleveland Clinic, said that the cancer link may not prove to be as strong as the well-documented relationship between sleep apnea and cardiovascular disease, “but until disproven, it would be one more reason to get your apnea treated or to get it diagnosed if you think you might have it.” In one of the new studies, researchers in Spain followed thousands of patients at sleep clinics and found that those with the most severe forms of sleep apnea had a 65 percent greater risk of developing cancer of any kind. The second study, of about 1,500 government workers in Wisconsin, showed that those with the most breathing abnormalities at night had five times the rate of dying from cancer as people without the sleep disorder. Both research teams only looked at cancer diagnoses and outcomes in general, without focusing on any specific type of cancer. Copyright 2012 The New York Times Company
Link ID: 16820 - Posted: 05.21.2012
by Debora MacKenzie OUR core physiology relies on subtle organic timers: disrupt them, and effects range from jet lag to schizophrenia. Exactly how and when life began keeping time is unclear, but a candidate for the original biological clock may solve the mystery. Biological clocks are ubiquitous in nature, so the first clock should pre-date the evolutionary parting of the ways that led to modern groups of organisms. All the clocks found so far are unique to different groups of organisms, though. Not so the clock discovered by Akhilesh Reddy at the University of Cambridge and colleagues. In an enzyme called peroxiredoxin (PRX), they seem to have found a grandfather clock - one that is common to nearly all life. PRX gets rid of poisonous, highly reactive oxygen (ROS), which is produced by oxygen-based metabolism. And the enzyme oscillates: it flits between an active and inactive state, depending on whether oxygen is bound to the active site. Using antibodies that bind only to the oxidised enzyme, the team found that PRX oxidation keeps cycling independently on a 24-hour cycle, even when organisms were kept in constant light or constant dark. Moreover, they found this PRX cycle in mice, fruit flies, a plant, a fungus, an alga, bacteria and even in archaea - the most primitive of all cellular life (Nature, DOI: 10.1038/nature11088). That suggests PRX evolved early in life's history. A gene sequence analysis suggests it did so 2.5 billion years ago, during the Great Oxygenation Event (GOE) - a critical interval when the oxygen released by photosynthesis began to accumulate in the atmosphere. © Copyright Reed Business Information Ltd.
By Jennifer Huget When my daughter was little, she was quite the sleepwalker. Until you have a sleepwalker in the family, you have no idea how terrifying it can be. You worry about whether they’ll safely navigate the stairs when they decide to sleep-stumble from the second-floor bedroom where they’re supposed to be, well, sleeping, to the first-floor family room where you’re watching TV. Or that they’ll open a door and wander outside in the middle of the night — and that you might not hear them leave. Or that they’ll pick up a knife in the kitchen or light a burner. . . . Let’s just say it’s hard to sleep with a sleepwalker around. And if you have ever tried to talk to a sleepwalking child, you know how worrying it is to see how completely out of it they seem. My son never walked in his sleep, and my daughter finally outgrew the behavior, which affects up to 30 percent of children, according to the introduction to a study published Monday afternoon in the journal Neurology. The new research set out to determine how common sleepwalking is among adults. According to the report, the phenomenon has been little studied, so data about its prevalence are quite limited. The best estimate before this new study was that between 2 and 3 percent of adults walk in their sleep; the new research puts the number of adults who have walked in their sleep at least once in the past year at 3.6 percent. And 29.2 percent of those surveyed reported having walked in their sleep at least once in their life. © 1996-2012 The Washington Post
Link ID: 16790 - Posted: 05.15.2012
by Erin Loury As if you needed another reason to despise your alarm clock. A new study suggests that, by disrupting your body's normal rhythms, your buzzing, blaring friend could be making you overweight. The study concerns a phenomenon called "social jetlag." That's the extent to which our natural sleep patterns are out of synch with our school or work schedules. Take the weekends: many of us wake up hours later than we do during the week, only to resume our early schedules come Monday morning. It's enough to make your body feel like it's spending the weekend in one time zone and the week in another. But is social jetlag actually bad for your health? To investigate, chronobiologist Till Roenneberg at the University of Munich in Germany and colleagues compiled data from tens of thousands of responses to an internet survey on sleep patterns and other behaviors. Previous work with such data has already yielded some clues. "We have shown that if you live against your body clock, you're more likely to smoke, to drink alcohol, and drink far more coffee," says Roenneberg. In the new study, the team measured the social jetlag of people ages 16 to 65 by calculating how offset sleep times were on workdays and non-workdays. They then constructed a mathematical model that gauged how well biological factors, such as age, gender, sleep duration, and social jet lag could predict body weight. They found that the first three factors were important predictors of body weight for all people. In addition, for people who are already on the heavy side, greater social jet lag corresponded to greater body weight. However, social jet lag was not a good predictor for people with normal body weights, the team reports online today in Current Biology. © 2010 American Association for the Advancement of Science.