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expert reaction to study on artificial light at night and obesity risk

Research published in JAMA Internal Medicine shows that exposure to artificial light at night was associated with increased risk of weight gain and overweight and obesity among a large group of women. 


Dr Michelle Miller, Associate Professor of Biochemical Medicine, University of Warwick, said:

“This is a large nationwide prospective cohort study of women aged 35-74years with a follow up of at least 5 years. It shows that even after adjustment for potential confounders that light exposure whilst sleeping is associated with obesity. It extends previous cross-sectional studies of light exposure and obesity.  The authors have adjusted for many potential confounders including sleep duration, which in this and previous studies has been prospectively associated with increased obesity, particularly in children. The study has a number of limitations: The study was only conducted in women;  measures of light exposure  were self-reported and  non-quantifiable and sleep duration was also self-reported. The findings are however consistent with current advice that sleeping environments should be as dark as possible.”


Prof Malcolm von Schantz, Professor of Chronobiology, University of Surrey, said:

“There are previous cross-sectional population studies showing that people who are exposed to light at night are more likely to be overweight. What is novel with this paper is that it is a longitudinal study comparing the weight of the same individuals at baseline and more than five years later.

“What they found was that individuals who reported that they had a light or a television on in their bedroom at night were 17% more likely to have gained more than 5 kg during the study period than those who were not exposed to significant amounts of light at night. The study would have been even stronger if the participants had been wearing instruments that measured their activity as well as the exact amount of light they were exposed to, rather than depending on self-report — but the findings make perfect biological sense. We know that light in the late evening will delay our body clocks. We know from experimental studies in people that light at night affects our metabolism in ways that are consistent with increased risk of metabolic syndrome.

“These new findings won’t change the advice to maintain good sleep hygiene, and avoid light and electronic distractions in the bedroom, but they add further strength to the case for this advice.”


Association of Exposure to Artificial Light at Night While Sleeping With Risk of Obesity in Women’ by Yong-Moon et al. was published in JAMA Internal Medicine at 16:00 UK time on Monday 10th June.


Declared interests

Prof Malcolm von Schantz: “I have no conflict of interest to declare.”

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