In the past 40 years, the average sleep duration among people in the US has decreased by 1–2 hours. At the same time, the prevalence of obesity has more than doubled, and nearly two-thirds of the US population is overweight. Could there be a connection?

Quite likely, according to a number of clinical studies that have found a dose-response relationship between shorter sleep duration and higher body mass index (BMI, a measure of overweight). In other words, as sleep decreases, BMI increases. But, until now, researchers could only speculate as to why sleep deprivation is associated with high BMI.

A new study in the December 2004 issue of PLoS (Public Library of Science) Medicine investigated the link between sleep duration and two appetite-regulating hormones—leptin and ghrelin. Leptin levels rise when you experience a calorie surplus, making you feel full. Ghrelin levels, on the other hand, rise in response to a calorie shortage, stimulating your appetite. This new study found that short sleep duration is not only associated with increased BMI, but also with reduced leptin levels and elevated ghrelin levels, which could—in theory—lead to weight gain.

About the Study

For this study, researchers used data and blood samples from the Wisconsin Sleep Cohort Study, an ongoing study of sleep habits and disorders in the general population.

For one part of the study, a sample of 1,024 participants came in for overnight stays in laboratory bedrooms, where their sleep habits were assessed with polsomnography, which uses a machine to monitor changes in brain wave, respiratory, and cardiac activity during the various stages of sleep. The researchers administered questionnaires on the participants’ lifestyle and health history (including the number of hours of “usual sleep” they get per night), measured their height and weight, and collected blood samples shortly after the participants awakened. The participants also kept a six-day diary to record the times they went to bed and arose each day.

The researchers calculated the participants’ BMI from their height and weight measurements, and recorded the levels of leptin and ghrelin in the participants’ blood samples to see if there was a link between sleep duration and levels of these hormones.

The Findings

The researchers found a significant relationship between average nightly sleep (calculated from the sleep diary) and BMI. Specifically, for people getting less than 7.7 hours of sleep (74% of the study population), increased BMI was proportional to decreased sleep.

Not surprisingly, low levels of leptin and high levels of ghrelin were also significantly associated with increased BMI. Moreover, sleep duration seemed to be connected with the hormone levels. Even after controlling for age, sex, BMI, and blood sample storage time, the researchers found that as average nightly sleep duration increased, so did leptin levels. And as total sleep time (as calculated by the polysomnography) increased, ghrelin decreased. In fact, a decrease from eight to five hours in average nightly sleep and total sleep time was associated with a 15.5% decrease in leptin levels and a 14.9% increase in ghrelin levels, respectively.

How Does This Affect You?

These findings suggest that too little sleep is associated with hormonal changes that could potentially lead to weight gain. Another new study in the December 2004 issue of the Annals of Internal Medicine supports these findings. In this study, 12 men slept in a laboratory setting for 10 hours two consecutive nights and for four hours two consecutive nights, with a six-week buffer period between. The participants completed questionnaires to assess their hunger and appetite, and the researchers measured levels of leptin and ghrelin in the participants’ blood. They found that sleep restriction was associated with an 18% decrease in leptin, a 28% increase in ghrellin, a 24% increase in hunger, and a 23% increase in appetite—especially for calorie-rich and high carbohydrate foods.

Does this mean doctors will soon be recommending more sleep for people who need to lose weight? Perhaps. While sleep deprivation alone cannot explain the increasing prevalence of overweight and obesity, it appears to be a significant factor, now supported by physiologic evidence. And weight loss, of course, isn’t the only potential benefit of getting enough sleep; sleep deprivation has been linked to decreased concentration, slowed reaction time, and even depression .

To help you sleep better, the American Academy of Family Physicians has the following suggestions:

  • Go to sleep and wake up at the same time every day—even on weekends
  • Develop a bedtime routine, such as taking a warm bath or reading for 10 minutes
  • Use your bedroom only for sleeping and sex—not balancing your checkbook or watching TV
  • Make sure your bedroom is quiet and dark