Exposure to light while sleeping linked to obesity: study

LONDON (Xinhua) - Women who are exposed to greater levels of light while sleeping tend more often to be obese, according to a British study published on Friday.

Scientists at the Institute of Cancer Research, London, found that body mass index, waist-hip ratio, waist-height ratio and waist circumference all increased with increasing exposure to light at night. They have published the findings in the American Journal of Epidemiology.

These associations were still seen after adjustments were made for confounding factors, which could be associated with light exposure levels and weight in the study participants such as physical activity, having young children and sleep duration.

However, the researchers cautioned that there is not enough evidence to advise people to buy thicker curtains or turn off the lights.

The results are taken from cross-sectional analyses of data from a major study, which followed more than 113,000 women in Britain for 40 years, in a bid to find the root causes of breast cancer. Obesity has been a known risk factor for breast cancer, but identifying underlying causes could help inform women how to manage their risk.

Prof. Anthony Swerdlow at the Institute of Cancer Research, London, and co-leader of the study, explained: "Metabolism is affected by cyclical rhythms within the body that relate to sleeping, waking and light exposure."

He added: "The associations we saw in our study between light exposure at night and obesity are very intriguing. We cannot yet tell at this stage what the reason for the associations is, but the results open up an interesting direction for research."