Chronic sleep deprivation may be part of America's obesity problem (search), a new study suggests. Lack of sleep has a bad effect on the "appetite control" hormone leptin, researchers say.

Leptin (search) is a widely studied hormone, thought to be the secret to obesity. Produced by fat cells, our leptin levels tell the brain when the body does or doesn't need more food.

Sleep deprivation plays an important role in regulating our leptin levels and in controlling appetite, explains senior researcher Eve van Cauter, PhD, a diabetes researcher with the University of Chicago. Her study appears in The Journal of Clinical Endocrinology & Metabolism this month.

A few earlier studies have investigated the effects of sleep deprivation (search) on leptin levels, since sleep regulates hormones and other body processes. During sleep, leptin levels normally rise. But leptin levels are also markedly dependent on sleep duration, she says.

According to the researchers, sleep deprivation results in a triggering of hormones of the nervous system, which can lower leptin levels. These low levels of leptin have been associated with obesity. Other hormones that control metabolism are also triggered by sleep deprivation and may affect leptin levels.

During periods of sleep deprivation, "low leptin levels tell the brain there is a shortage of food and increase appetite," van Cauter tells WebMD. "When leptin levels are higher, satiety levels are higher, which tells the brain that the body is getting enough food."

In their study, van Cauter's research group investigated sleep deprivation's effects more closely.

Sleep Deprivation and Leptin

The study involved 11 healthy 22-year-old men who spent 16 consecutive nights in the University of Chicago's sleep laboratory. For six days they got four hours of sleep -- their week of sleep deprivation.

The men's food and activity levels were strictly regulated and hormone levels were taken during the day and while they slept. Their sleep was also monitored to make sure they followed the study's guidelines.

One year later, the men returned for a six-day study with an 8-hour sleep period, so they served as their own comparison group, van Cauter explains.

The results: After their six-day sleep deprivation period, volunteers had a leptin decrease ranging from 19 percent to 26 percent, she reports.

The decrease appears to send an erroneous signal from the brain that more food is needed when, in fact, enough food has been eaten, says van Cauter.

This suggests that during periods of sleep deprivation, we tend to overeat," van Cauter tells WebMD. Since the men were getting the same amount of calories and activity, leptin levels and appetite control should not have changed. "But, in fact, they changed in a major way."

Some volunteers were asking for up to 1,000 calories more per day, van Cauter reports. "We think sleep deprivation probably signals a need for additional calories."

A larger study, involving more than 1,000 volunteers, showed a similar appetite control pattern.

More Than Sleep Deprivation Affects Leptin

Satya P. Kalra, MD, professor of neuroscience at the University of Florida in Gainesville, is conducting his own leptin research. He offers his insights on this aspect of sleep deprivation.

"Sleep is not the primary regulator of leptin," Kalra tells WebMD. Sleep deprivation "is one of many factors that can affect leptin. But leptin is produced by fat cells, and most leptin production is dependent on the amount of calories one consumes and burns. If there is excess calorie intake, that excess is stored as fat. That fat produces more leptin,"

It's true, a decrease in leptin increases appetite, as van Cauter showed during sleep deprivation, Kalra says. However, her study is by no means conclusive, he says. A few other studies have shown that sleep deprivation creates eating disorders.

Until scientists have this theory worked out, there's no denying that getting sufficient sleep is a good idea. Sleep deprivation is simply stressful on the body overall. "Our study suggests that if you are trying to lose weight by restricting calories when you aren't getting enough sleep, it's probably going to be very difficult to lose weight," says van Cauter.

Also, a number of studies have shown a relationship between body mass index (BMI, an indirect measure of body fat) and sleep deprivation, she adds. "These consistently suggest that when sleep is under seven hours, BMI is higher."

By Jeanie Lerche Davis, reviewed by Brunilda Nazario, MD

SOURCES: Van Cauter, E. The Journal of Clinical Endocrinology & Metabolism, November 2004; vol 89: pp 5762-5771. Eve van Cauter, PhD, University of Chicago. Satya P. Kalra, MD, professor of neuroscience, University of Florida, Gainesville.