If your New Year’s resolution includes losing some weight, it’s a safe bet that exercising more is high on your list of priorities. But if your plans include skipping some sleep to get in those trips to the gym, you could be undermining your weight loss plan before you get started.

A growing number of Americans are both overweight and sleep deprived (search), and there is mounting evidence that the two are related. Several recent studies have suggested that sleep deprivation may at least partially explain the epidemic of obesity in the U.S. (search), and now new research strengthens the argument.

Sleep Times Predicted Weight

Investigators surveyed roughly 1,000 people about their sleep patterns and also determined if they were normal weight, overweight, or obese by calculating their body mass index. Total sleep times tended to decrease as body weight increased, with the exception of people who were morbidly obese.

The difference in total sleep time between patients who were normal weight and those who weren't was only 16 minutes per day, or 1.86 hours over a week.

The findings are reported in the Jan. 10 issue of the Archives of Internal Medicine.

Lead researcher Robert D. Vorona, MD, says even though his study does not prove that sleep deprivation leads to obesity, the research as a whole certainly points in that direction. Vorona is an assistant professor of internal medicine and a sleep specialist at Eastern Virginia Medical School.

“Obviously there are reasons besides curtailed sleep to explain why Americans are increasingly obese,” he tells WebMD. “Lack of exercise, supersized portions, and other things are certainly important. But it is also very possible that the reductions in sleep that so many of us are experiencing may also be playing a role.”

Sleep, Obesity 'A Two-Way Street'

According to a poll conducted in 2000 by the National Sleep Foundation (search), the average American gets just under seven hours of sleep each night -- about an hour less than is optimal for most people. That is about 90 minutes less than Americans tended to sleep in the early 1900s.

Psychologist Michael Breus, PhD, who specializes in treating sleep problems, tells WebMD that sleeping eight hours or more each night doesn’t necessarily mean a person isn’t sleep deprived. Obese people often suffer from sleep apnea (search), a condition characterized by repeated waking during the night leading to poor-quality sleep.

“It really does appear that sleep and obesity are a two-way street,” he says. “Bad sleep may lead to weight gain, and weight gain can lead to bad sleep.”

Recent studies suggest that sleep deprivation plays a role in the secretion of appetite-regulating hormones, increasing levels of a hormone that triggers hunger and reducing levels of one that signals fullness.

Eat Less, Exercise, and Get Those Zzzs

So is it time to include “Get more sleep” in the dieter’s mantra of “Eat less and exercise more”? The experts say yes.

Fred Turek, MD, who directs the sleep center at Northwestern University, says raising public awareness about the link between sleep deprivation and weight is a top priority because obesity is a leading cause of death and illness in America.

“Sleep is really a behavior that has been ignored,” he tells WebMD. “Everybody talks about diet and exercise, but nobody pays much attention to sleep.”

Vorona says he hopes to get funding for an intervention study to measure the impact of sleep times on the success or failure of people trying to lose weight.

“If we were able to show that increasing sleep actually aids in weight loss, that would go a long way to proving cause and effect,” he says.

By Salynn Boyles, reviewed by Brunilda Nazario, MD

SOURCES: Vorona, R. Archives of Internal Medicine, Jan. 10, 2005; vol 165: pp 25-30. Robert D. Vorona, MD, assistant professor of internal medicine, Eastern Virginia Medical School, Virginia Beach, Va. Michael Breus, PhD, sleep medicine specialist, Atlanta. Fred Turek, MD, professor and director of the Center of Sleep and Circadian Biology, Northwestern University Feinberg School of Medicine, Evanston, IL.