Results indicate that twins who slept between 7 and 8.9 hours each night had a lower mean BMI (25.0 kg/m2) compared to those who regularly slept either more (25.2 kg/m2) or less (26.4 kg/m2) per night. The relationship between sleep duration and BMI remained after controlling for genetics and shared environment.

According to the lead author of the story, Nathaniel Watson, MD, co-director at the University of Washington Sleep Institute, in Seattle, sleep habits have a significant impact on weight and BMI.

"Findings of the study point towards an environmental cause of the relationship between sleep duration and BMI," said Watson. "Results were robust enough to be present when the sample was limited to identical twins."

The study included data from 1,797 twins, including 634 twin pairs (437 monozygotic, 150 dizygotic and 47 indeterminate pairs) and 529 individual twins with a mean age of 36.8. Habitual sleep duration was obtained by self-reported length of sleep per night and BMI was calculated by self-reported height and weight. Of the sample, 68.3 percent female, 88.2 percent were Caucasian. Results persisted in a co-twin control analysis of within twin pair differences in sleep duration and BMI.

Abstract Title: Does Sleep Duration Influence Body Mass Index in Twins?

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Materials provided by American Academy of Sleep Medicine. Note: Content may be edited for style and length.