New research could explain why you’re so darn tired all the time — and lead you to the solution. (Photo: Getty Images/Photodisc)

If you’re constantly trying not to doze off and are always daydreaming about your bed (oh, your perfect, cozy, warm bed…), you’re not the only one. Many people feel tired during the day — and lack of sleep isn’t always the reason.

Researchers from Penn State College of Medicine have found that both obesity and depression are underlying causes for chronic drowsiness. The revelation may lead to more personalized treatments for excessive daytime sleepiness, or the inability to stay alert during the day. Studies estimate the condition affects between 11 to 25 percent of the population.

In the new study, more than 1,300 people spent a night being observed in a sleep lab, and then underwent a physical exam and filled out surveys on their sleep habits and well-being. After about 7.5 years, on average, the researchers followed up with telephone interviews to check in on the study participants’ health and sleep.

The results, published in the journal SLEEP, showed that gaining weight and being obese were linked with excessive daytime sleepiness. Losing weight, on the other hand, was associated with relief from the condition over time.

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In addition, researchers found that the link between sleepiness and body mass index (a measure of weight relative to height) wasn’t related to how much the subjects slept. In other words, obese people may be tired during the day no matter how much they sleep at night.

Obese people are likely to deal with extreme fatigue from having low-grade chronic inflammation, according to the study. Fat cells, particularly from abdominal fat, produce immune compounds called cytokines that promote sleepiness.

People who were depressed and reported sleep disturbances, such as taking a long time to fall asleep and waking up in the middle of the night, also had an increased risk for EDS. This may be due to elevated stress hormones.

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These findings should change the one-size-fits-all treatment for excessive daytime sleepiness, which is sleeping pills, says lead study author Julio Fernandez-Mendoza, PhD, of the Sleep Research & Treatment Center at Penn State College of Medicine.

“Persons who are obese and complain of daytime sleepiness require a thorough evaluation because sleep apnea or other sleep disorders may be present and should also be addressed,” Fernandez-Mendoza tells Yahoo Health. He adds that weight loss through diet, physical activity, and behavioral change (such as managing emotional eating), “should be a priority to reduce body weight and daytime sleepiness.”

If you think your daytime fatigue may be linked to depression, visiting a psychiatrist or psychologist for an official depression diagnosis is the first step, Fernandez-Mendoza says. "Many individuals with complaints of daytime sleepiness who are depressed may require specific treatment for their sleep disturbance, which can be accomplished with cognitive-behavioral treatment for insomnia or sleep medication,” he adds.

Also talk with your family doctor if you feel zonked during the day, most days. “Your family doctor will know how you should be managed and which type of clinician will be best,” Fernandez-Mendoza says. You may need to be evaluated at a sleep disorders center, where a team of specialists can evaluate and treat the underlying cause of your sleep disturbances.

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