Being obese or depressed may make you more likely to be sleepy during the day, new research shows. About 20% of American adults have excessive daytime sleepiness, according to the National Sleep Foundation.

Although poor sleep is often blamed for excessive daytime sleepiness, ''we found that depression and obesity were the strongest risk factors for being tired and sleepy," says Alexandros Vgontzas, MD, a professor of psychiatry at Penn State.

He presented three studies on daytime sleepiness this week at Sleep 2012, the annual meeting of the Associated Professional Sleep Societies in Boston.

The good news: "If you lose weight, you are going to be less tired and sleepy," says Vgontzas. In one of the studies, he found that as people lost their extra pounds, they became less sleepy during the day.

Slideshow: Surprising Reasons You're Gaining Weight
Daytime Sleepiness Studies

One study included 1,173 adults who weren't excessively sleepy during the day.

Researchers tracked their BMI and health conditions such as high blood pressure or depression for the next seven years. They also tested them for sleep apnea, a disorder in which people have episodes when they stop breathing during sleep.

Sleep apnea and poor sleep are often blamed for excessive daytime sleepiness.

During the study, 138 people (8%), developed excessive daytime sleepiness.

The odds of developing excessive daytime sleepiness were:

    Nearly three times as high in depressed people
    More than twice as high in obese people and people with sleep apnea

Vgontzas' second study showed that, among obese people, excessive daytime sleepiness was more likely to be persistent in people with higher BMI. And it was a cycle: People whose excessive daytime sleepiness persisted were more likely to gain more weight.

"Obesity and depression are significant risk factors for new-onset excessive daytime sleepiness or to keep on having it if you have it," Vgontzas tells WebMD.

A third study included 103 men and women who were overweight on average who were studied in a sleep lab and screened for depression.

"Those who were sleeping longer at night were also sleeping during the day," Vgontzas tells WebMD. "This goes against the concept of sleep deprivation [as the trigger for excessive daytime sleepiness]."

In this study, waist circumference and depression most strongly predicted their subjective sleepiness.
Second Opinion

The findings make sense, says Alon Y. Avidan, MD, MPH, associate professor of neurology and director of the Sleep Disorders Center at the David Geffen School of Medicine at the University of California, Los Angeles. He reviewed the findings for WebMD.

He has noted weight loss in some of his patients leading to less daytime sleepiness, he tells WebMD. "From my own patients, patients who undergo bariatric surgery, a week or two after, they report to me their daytime sleepiness declines," he says.

The findings, he says, are "not new in the sense that we knew excessive weight gain certainly put people at risk of daytime sleepiness."

But the new research more strongly links BMI with the daytime sleepiness, he says.

The new research suggests that if people lose weight they may not only reduce their risk for depression and sleep apnea (a sleep problem that is more likely with excess weight) but also have more energy, Avidan says.

Avidan is a speaker for Teva, which makes modafinil, a treatment for excessive sleepiness.