September 29, 2006

Obesity Reduces Sleep Duration
(Reuters Health)

In rural populations, the amount of time spent sleeping falls as BMI goes up, study results suggest.

Previous studies conducted in urban and suburban areas have had similar results, which suggest that sleep loss may play a role in the increasing rates of obesity in the US. Researchers have proposed that shorter sleep duration may lead to reduced levels of leptin, a hormone associated with satiety, and increasing levels of ghrelin, associated with hunger.

Dr. Neal D. Kohatsu, an epidemiologist at the California Department of Health Services in Sacramento, and his associates were interested in studying rural populations because obesity rates are higher and lifestyle patterns of nutrition, physical activity, work hours, and sleep differ from those in more populous areas. Rural populations also have a higher prevalence of suicide and a greater propensity toward other risky health behaviors.

Furthermore, according to their report in the Archives of internal Medicine for September 18, theirs is the first study evaluating the relationship between sleep duration and BMI in rural settings.

They therefore conducted a cross-sectional analysis of data collected between 1999 and 2004 in an agricultural county in southeastern Iowa. A random sample of 990 employed adults were surveyed. The subjects were asked about sleep duration, physical activity associated with employment, depressive symptoms, alcohol consumption, snoring, and other demographic information. Height and weight were measured during the same visit.

As noted, there was a linear relationship, with BMI negatively correlated with sleep duration. Their data show that average BMI ranged from 30.24 kg/m² among individuals sleeping less than 6 hours/night, to 28.25 among those who sleep more than 9 hours at a time.

In a multivariate analysis adjusting for the information collected in the surveys, BMI remained a significant correlate with the amount of time spent sleeping.

Dr. Kohatsu's group speculates that "modest but sustained changes in sleep duration could have a clinically significant effect on weight."

But they also acknowledge that "the cross-sectional design precludes determination of causality."

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