Physiology

Working on Borrowed Time

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Science  01 Jun 2012:
Vol. 336, Issue 6085, pp. 1080
DOI: 10.1126/science.336.6085.1080-c
CREDIT: THINKSTOCK

Many of us are sleeping less than we used to because of the demands of work and the enticements of the Internet, television, and digital social networking. It is also true that we are increasingly sleeping outside of the times normally dictated by our internal circadian clocks (our “chronotype”). This difference between circadian and social clocks has been termed “social jet lag.”

Roenneberg et al. have analyzed data from the Munich ChronoType Questionnaire (MCTQ), which assesses sleep behavior on work and free days. They calculated that one-third of the 65,000 European participants in the MCTQ suffered from at least 2 hours of social jet lag, with teenagers suffering the largest deficiencies. Reduced amounts of sleep are known to be correlated with increased body mass index (BMI) and obesity—the results showed that social jet lag is an equally important predictor of BMI. Furthermore, the average chronotype has shifted later into the night over the past decade, exacerbating social jet lag. This change in chronotype has probably been driven by a weakening of the external cues that normally entrain our circadian clocks—increasing numbers of people living and working in cities being exposed to less light during the day and more light during the night, and spending less time outdoors. People who regularly sleep outside of their circadian window can show an imbalance in glucose metabolism normally associated with type 2 diabetes.

Curr Biol. 22, 10.1016/j.cub.2012.03.038 (2012).

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