A study published in the February 2010 issue of SLEEP* found that short sleep duration (less than 6 hours/night), as well long sleep duration (more than 9 hours/night) were associated with increased weight gain in men.
More than 35,000 workers at an electric power company in Japan (of whom 31,000 were men) were followed over the course of a year, with weight, height, and self reported sleep duration obtained at annual health checkups in 2006 and 2007. Out of those men who were not overweight at the beginning of the study, 5.8% became so during the study period.
What was interesting was that men who slept fewer than 5 hours/night were almost twice (1.91 times) as likely to have become overweight during that time than those who were considered normal, and who slept between 7-8 hours/night. Those men sleeping between 5-6 hours/night were one and a half times more likely to have become overweight relative to the 7-8 hour/night group. Men sleeping more than 9 hours/night were 1.42 times more likely to have become overweight as compared with the 7-8 hour/night group. While no similar, statistically significant finding was found amongst the women, it is important to point out that the numbers of women sleeping 5-6 hours/night (14) and fewer than 5 hours/night (1) were very small.
How can one explain the connection between short sleeping and weight gain? One reason is that insufficient sleep is well known to affect the secretion of certain hormones called ghrelin and leptin, which govern both the sensation of hunger and of feeling full. When this is disrupted, we tend to eat more, and feel less full when we do.
Another reason for the connection may be co-existing depression, which very often causes loss of sleep (though in some cases it can lead to oversleeping), and its treatment with certain medications which may cause weight gain. Whereas 2.3% of those sleeping 7-8 hours/night had depressive symptoms, 6.7% of those sleeping fewer than 5 hours/night, 3.8% of those sleeping 5-6 hours/night and 4.9% of those sleeping greater than 9 hours/night had depressive symptoms. That being said, insufficient sleep itself can lead to depressive symptoms, so it is not clear which is cause and which is effect.
In summary: this study provides one more piece of evidence demonstrating just how important sleep is to staying healthy. It also shows why one should make a conscious effort to getting a good night's sleep, and not just treat it like something to be left for when one has run out of other, more "important" things to do.
Dennis Rosen, M.D.
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* Watanabe M; Kikuchi H; Tanaka T; Takahashi M. Association of short sleep duration with weight gain and obesity at 1-year follow-up: a large-scale prospective study. SLEEP 2010;33(2):161-167.