Rambo Tribble writes: Writing in the American Journal of Epidemiology, researchers have found that sleeping with high ambient light levels may contribute to obesity [Abstract; paywall]. In a large survey, of 113,000 women, a high correlation was found between higher bedroom light levels and increased propensity to overweight or obesity. Excess light in the sleeping environment has long been known to adversely affect melatonin production and circadian rhythms. It is posited that such an interference with the "body clock" may be behind these results. Although there is not yet enough evidence to call this a smoking gun, as one researcher put it, 'Overall this study points to the importance of darkness.' The BBC offers its take on the story, here.