People who don't sleep very long are more likely to be overweight. But that doesn't necessarily mean that sleep deprivation makes you fat—it could be that both are caused by being a couch potato, by eating badly, or by something else entirely. Researchers at Stanford and the University of Wisconsin–Madison looked at how sleep deprivation affects levels of hormones that regulate appetite.

What the researchers wanted to know: What's the relationship between sleep, body mass index, and metabolic hormones?

What they did: The researchers used the Wisconsin Sleep Cohort Study, a long-term study of sleep habits and sleep disorders in thousands of people who worked for the state in 1989. Many respondents just fill out a questionnaire every few years, but over 1,000 have spent a night in the lab, and most of those have had a blood sample taken after a night of sleep.

What they found: People who slept for shorter times had higher levels of ghrelin (a hormone that increases appetite) and lower levels of leptin (a hormone that suppresses appetite). So both hormones changed in the direction that would encourage more eating. People with short sleep also had higher body mass index.

What the study means to you: This could be one way to help prevent or treat obesity, the researchers write.

Caveats: Leptin and ghrelin were measured only once a day—after the subjects woke up—so this may not reflect levels of the hormones over the entire day.

Find out more: Use this website (www.menschenskinder-online.de) to teach yourself Brahms' Lullaby in the original German. Will it help you lose weight? Probably not. But it's kind of fun.

Use our BMI calculator to calculate your body mass index.

Read the article: Taheri, S., et al. "Short Sleep Duration Is Associated With Reduced Leptin, Elevated Ghrelin, and Increased Body Mass Index." PLoS Medicine. December 2004, Vol. 1, No. 3, e62.

Read the full report: www.plosmedicine.com (PDF)