Shorter sleep durations may increase genetic risks for obesity

Results of a study of 1,811 pairs of twins show that the heritability of sleep duration was 32 percent, and shared environmental influences on sleep duration were negligible. Longer sleep duration was associated with decreased body mass index, which is a measure of body fat based on height and weight.

Behavioral genetic modeling found significant interactions between self-reported, habitual sleep duration and both genetic and shared environmental influences on BMI. The heritability of BMI when sleep duration equaled seven hours was more than twice as large as the heritability of BMI when sleep duration equaled nine hours.

"The heritability of body weight decreased as sleep duration increased," said principal investigator Dr. Nathaniel Watson, associate professor of neurology at the University of Washington and co-director of the UW Medicine Sleep Center. "There appears to be something about short sleep that creates a permissive environment for expression of obesity-related genes."

The study involved a population-based sample of 1,811 pairs of identical and fraternal twins from the University of Washington Twin Registry. They had a mean age of about 37 years. Height, weight and habitual sleep duration were collected by self-report surveys. Participants were slightly overweight with a mean BMI of 25.4, and they had a mean sleep duration of about seven hours and 11 minutes per night. Data were analyzed using behavioral genetic interaction models.

According to Watson, the study is an important addition to the existing body of research on the relationship between sleep duration and BMI.

"Epidemiological and experimental studies have shown short sleep is associated with obesity," said Watson. "Our work takes this a step further, showing that short sleep facilitates expression of obesity-related genes."

The authors concluded that future research aiming to identify specific genotypes for BMI may benefit from considering the moderating role of sleep duration.

In a smaller study of 612 twin pairs published in the Journal of Clinical Sleep Medicine in 2010, Watson found that short sleep was associated with elevated BMI following careful adjustment for genetics and shared environment. In a study published in JAMA in 2010, the CDC estimated that 68 percent of U.S. adults were overweight or obese in 2007 -- 2008.