New research co-funded by Breakthrough Breast Cancer has found that women who are exposed to greater levels of light while sleeping tend more often to be obese.
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. The findings were published in the American Journal of Epidemiology.
These associations were still seen after adjustments were made for confounding factors that could be associated with light exposure levels and weight in the study participants, such as physical activity, having young children and sleep duration.
These results are taken from cross-sectional analyses of data from the Breakthrough Generations Study, the largest study of its kind, following more than 113,000 women from across the UK for 40 years in a bid to find the root causes of breast cancer. Obesity has for some time been a known risk factor for breast cancer, but identifying underlying causes and how they come about could help inform women how to manage their risk in the future.
The study was funded by Breakthrough Breast Cancer and The Institute of Cancer Research (ICR), with additional support from the NIHR Biomedical Research Centre at The Royal Marsden NHS Foundation Trust and the ICR.
Professor Anthony Swerdlow, Professor of Epidemiology at the ICR, and co-leader of the study, said: “Metabolism is affected by cyclical rhythms within the body that relate to sleeping, waking and light exposure.
“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. The contributions of more than 100,000 women in the UK to the Breakthrough Generations Study have been critical to this.”
Dr Emily McFadden, Visiting Researcher at the ICR, and first author of the paper, said: “We examined the association between light exposure and obesity cross-sectionally in over 100,000 women from the UK Breakthrough Generations Study.
"Because all the information was collected at the same time, we cannot tell the sequence of events, but the associations we found are consistent with previous research examining light exposure and metabolism, and further investigation is needed."
Dr Matthew Lam, Senior Research Officer at Breakthrough Breast Cancer, said: “These findings add weight to previous results from animal studies that looked into how light exposure, circadian rhythms and metabolism could all be connected in some way. It’s too early to suggest that sleeping in the dark will help prevent obesity, a known risk factor for breast cancer, but the association is certainly interesting.
"Whilst we are learning more and more each day about the environmental, genetic and lifestyle factors that affect breast cancer risk, it is not yet possible to predict who will get breast cancer, and for women who have been diagnosed with the disease, we can’t yet say what caused it.
"That’s why Breakthrough is leading the way to find the answers to these questions through our research work. Our hope is that as the Breakthrough Generations Study continues to report over time, we will eventually be able to identify high-risk women and find ways to prevent them from developing breast cancer at all."