Can light in the bedroom at night drive weight gain?

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I came across and interesting report today, published on the BBC website here. In essence, this study found that in a large group of women, the more light they tended to have in their bedrooms at night, the heavier they tended to be [1]. This is an ‘epidemiological’ evidence, and does not prove therefore that light exposure at night causes weight gain. However, is it possible that ‘light pollution’ at night may drive weight gain? Also, might ensuring genuine darkness at night assist weight control or even weight loss?

In a recent blog post I made the point that light exposure during the day generally helps to promote good sleep, but it has quite the opposite effect in the evening and at night. This is plenty of evidence now that shows that sleep disruption can have biochemical, physiological and metabolic effects that have the capacity to promote fat deposition in the body.

The effect of light exposure at night has been tested in animals. In one study, light exposure at night was found to suppress secretion of growth hormone – a hormone, which among other things, promotes ‘lipolysis’ (fat loss) [2].

In another study, exposing mice to light at night caused them to rapidly gain weight, even though light did not cause them to consume more food over the day [3]. A pdf of this study can be found here. In it, the authors reference much evidence regarding the impact of light at night on health in not just animals, but humans too.

The relationship between light, sleep, physiology and health is highly complex. However, as a general rule I think it’s fair to say we are probably helping ourselves by getting adequate light exposure during the day, but keeping our exposure to light exposure at night to a minimum. The first requirement here can often be met by being mindful of the importance of light and ‘getting out more’ when conditions allow.

For the second, some might consider investing in appropriate blinds or curtains. Another option, though, is to make use of eyeshades. I’ve found these vary enormously in terms of comfort and effectiveness. However, if you find a pair that work for you, this relatively small investment may pay back big in terms of your overall health in time.


1.    McFadden E, et al.The Relationship Between Obesity and Exposure to Light at Night: Cross-Sectional Analyses of Over 100,000 Women in the Breakthrough Generations Study Am. J. Epidemiol. first published online May 29, 2014

2.    Kasuya E, aet al. Light exposure during night suppresses nocturnal increase in growth hormone secretion in Holstein steers.vJ Anim Sci. 2008;86(8):1799-807

3.    Fonken LK, et al. Dim light at night disrupts molecular circadian rhythms and increases body weight. J Biol Rhythms. 2013;28(4):262-71.

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