By Melissa S. Lim, M.D., FAASM
Globally, more than one billion adults are classified as overweight (body mass index (BMI) of 25 to 29.9 kg/m), or obese (BMI > 30 kg/m). While some contributing factors to the obesity epidemic are well recognized—genetic background, physical inactivity, consumption of high-fat or high-carbohydrate foods—the role of sleep is often overlooked. Over the last 30 years, sleep duration in the general adult population has decreased from 8.5 hours to 7.2 hours and sleep complaints are common.
Today, approximately 25% of the U.S. population is sleep deprived. As our sleep duration has decreased, rates of obesity have increased. Studies suggest that sleep deprivation alters metabolism in a manner that predisposes to weight gain. Leptin, the hormone that regulates body adiposity, and ghrelin, an orexigenic peptide hormone primarily secreted by the stomach, play a major role in appetite control, food intake and weight regulation. These hormones are central to the sleep duration/BMI relationship: sleep restriction decreases leptin and increases ghrelin, thus increasing appetite levels, which can lead to obesity.
A Brief Look at Recent Studies
A recent study by Theorell-Haglöw et al. (Associations between short sleep duration and central obesity in women, Sleep. 2010 May 1;33(5):593–598), was the first to use full-night polysomnography rather than self-reported sleep duration to demonstrate a significant inverse association between sleep duration and waist circumference, a marker of central obesity that is more strongly related to cardiovascular disease, type 2 diabetes mellitus and mortality than BMI. Sleep duration was inversely related to both waist circumference and sagittal abdominal diameter. These associations were stronger in younger women (age <50). These findings may suggest that it is possible to lose weight while sleeping.
In a Japanese study by Watanabe et al.( Association of short sleep duration with weight gain and obesity at 1-year follow-up: a large-scale prospective study, Sleep, 2010 Feb 1;33(2):161–167), short sleep duration was associated with weight gain and the development of obesity in men. The study included 35,247 company employees (31,477 men; 3,770 women), who underwent measurements of weight and height, and reported sleep duration, at annual health checkups in 2006 and 2007. Short sleep duration (< 5 and 5–6 h) and long sleep duration > or = 9 h were associated with an increased risk of weight gain among men after adjustment for covariates. Of the non-obese (BMI < 25) men at baseline, 5.8% became obese (BMI > or = 25) 1 year later. Higher incidence of obesity was observed among groups with shorter sleep duration. Adjusted odds ratios for the development of obesity were 1.91 (95% CI 1.36, 2.67) and 1.50 (95% CI 1.24, 1.80) in men who slept < 5 and 5–6 h, respectively.
Take Home Points:
- Insufficient sleep is a rapidly growing health problem globally.
- There are many causes of insufficient sleep (sleep apnea, insomnia, circadian rhythm disorders) that may warrant further evaluation.
- Sleep deprivation causes hormonal changes that alter metabolism and increase appetite.
- Studies suggest that insufficient sleep increases the risk of obesity.
Well, for those of us thinking we might trim down by simply adding an hour or so of sleep back into our daily routine, the solution may not be quite that simple. More studies are needed to determine the nature and direction of the association between sleep and obesity. It is clear though, that the obesity epidemic requires a multidisciplinary approach including stress management, reduction of risky behaviors, and an increase in healthy lifestyle habits—and one of those healthy habits, adequate sleep, may be key factor in the equation.
Melissa S. Lim, MD, is the Medical Director and founder of Redwood Pulmonary Medical Associates. Dr. Lim is board certified in internal medicine, pulmonary diseases, and sleep medicine.