In another finding among the nurses, those who slept nine or more hours a night were twice as likely to develop Parkinson's disease as those who averaged six hours or less. This study, by scientists at the National Institutes of Health, tracked 80,000 nurses, all initially free of the disease, for 24 years.
Though it seems counterintuitive, people who sleep less tend to weigh more. After adjusting the data for all sorts of potentially confounding factors, researchers who studied 990 employed adults in rural Iowa found that the less sleep they received on weeknights, the higher their body mass index.
Shahrad Taheri of the University of Bristol in England noted that in a long-term UK study, "short sleep duration at an early age of 30 months predicts obesity at age 7." Taheri suggested last year in The Archives of Disease in Childhood that sleep loss in toddlers might change brain mechanisms that regulate appetite and energy expenditure.
In the Wisconsin Sleep Cohort Study, short sleep duration was associated with low levels of leptin, a hormone that signals the need for more calories. In addition, short sleepers had higher levels of the hormone ghrelin, which is released mainly in the stomach at highest levels before meals and has been shown to increase food intake.
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