For years, experts have warned that obesity increases the risk of diabetes, hypertension and heart attack. Now, there's more bad news: Being fat makes it harder to sleep, and sleep deprivation can increase your craving for food.
Recent studies at the Johns Hopkins University and elsewhere show that those who sleep poorly are more likely to have weight problems than sound sleepers, that high-fat diets can alter sleep cycles and that hormones controlling our appetites can rise and fall with the quality of our shut-eye.
"If you don't sleep well tonight, you're going to have trouble driving tomorrow. The question is, is there a bigger payback than that?" said Dr. Naresh Punjabi, a sleep researcher at the Johns Hopkins Bayview Medical Center.
Sleep is an increasingly scarce commodity in today's caffeinated world. Only half of all U.S. adults said they consistently got seven to eight hours of sleep in a 2005 survey by the National Sleep Foundation. Nearly one in six said they got less than six hours a night - a 33 percent increase from the survey's first report in 1998.
One reason: too many distractions.
"There's the Internet, all-night shopping. We're so busy; we have so many responsibilities with our work life, our home life. A lot of people are choosing not to sleep so much," said James Gangwisch, an epidemiologist who researches sleep habits at Columbia University.
Junk food and a lack of exercise are obvious culprits in the nation's obesity epidemic. But would obesity be less of a problem if people addressed their sleep problems before gaining those extra pounds?
"The information we have suggests that might be the case," said Michael Twery, director of the National Center on Sleep Disorders Research, which is part of the National Heart, Lung, and Blood Institute.
The NHLBI has spent $20 million since 2003 on 14 studies exploring ways that sleeping problems contribute to obesity and other health issues/
Dr. Giovanni Cizza, a National Institutes of Health researcher in Bethesda, has enrolled 45 volunteers from the Baltimore-Washington area so far in a study to see whether obese patients with sleep problems will lose more weight than a control group by improving their sleep habits during a year of dieting.
Volunteers have so far extended their shuteye an average of 40 minutes a night by following basic techniques such as minimizing their use of caffeine and alcohol and skipping daytime naps, Cizza said.
"They're already saying they feel better, they're less cranky and they're more focused during the day," said Cizza, a researcher with the National Institute of Diabetes and Digestive and Kidney Diseases. He hopes to enroll 105 more volunteers and have preliminary results by July 2008.
Experts say the link between obesity and sleep deprivation is a logical one: If you don't sleep well, you're less likely to exercise and maintain a healthy diet.
Obesity also increases the risk of sleep apnea, a common disorder in which the airway is repeatedly obstructed during sleep, making it difficult to breathe.
"Does being obese put you at risk of sleep disorders? Yes. But the fact is there's a lot going on in obesity," said Dr. Steven M. Scharf, a pulmonologist who is director of the University of Maryland Sleep Disorders Center.
Dawn Fitzpatrick, a 40-year-old Baltimore special education teacher, knows that all too well. In 2002, she slept each night sitting in a chair because at 305 pounds, she had too much trouble breathing when she tried to lie down in bed. She started gaining weight about 15 years ago and began having sleeping problems in the late 1990s.
"I was always tired, and I didn't know why," said Fitzpatrick.
In 2002, doctors conducted a sleep study - a test in which they observed her sleep patterns. They discovered that she was waking up more than 30 times throughout the night. After a series of emergency room visits and a dizzy spell in 2002, she was diagnosed with heart failure and began an intensive effort to improve her cardiac health.
Gastric bypass surgery at Sinai Hospital in 2004 ultimately helped bring her weight down to about 160 pounds. Fitzpatrick is now on a low-fat, low-sodium diet and sleeping six to seven hours a night.
"I'm half of what I was before," she said. "The sleep apnea has dissipated, and I'm sleeping much better."
But some experts remain skeptical of studies that link obesity and sleep. None has proved a cause-and-effect relationship between sleep loss and weight gain, they note.
"It's very suggestive and very interesting work, but nothing has been firmly established," said Dr. Lawrence Cheskin, director of the Johns Hopkins Weight Management Center.
Still, researchers have uncovered intriguing evidence of a possible hormonal connection. Scientists at the University of Chicago found in 2004 that when 12 young men slept only four hours a night for two nights, it raised their levels of a hunger-stimulating hormone called ghrelin and lowered levels of leptin, a hormone that can suppress hunger.