Women who are exposed to greater levels of light while sleeping tend more often to be obese, according to new research from The Institute of Cancer Research, London.
Co-funded by Breakthrough Breast Cancer, the research found that body mass index, waist-hip ratio, waist-height ratio and waist circumference all increased with increasing exposure to light at night
The associations were still observed 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.
Findings, published in American Journal of Epidemiology, were taken from cross-sectional analysis of data from the Breakthrough Generations Study, which aims to uncover the root causes underlying breast cancer. The study is following more than 113,000 women from across the UK and will run for the next 40 to 50 years.
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 findings from this study add weight to previous results from research in animals.
First author of the paper, Dr Emily McFadden, Senior Epidemiologist/Medical Statistician at the Nuffield Department of Primary Care Health Sciences, University of Oxford, who was a Visiting Researcher at the Institute of Cancer Research London at the time of the study 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."
Professor Anthony Swerdlow, Professor of Epidemiology at The Institute of Cancer Research, London, 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.”
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.
McFadden E, Jones ME, Schoemaker MJ, Ashworth A, Swerdlow AJ. The Relationship Between Obesity and Exposure to Light at Night: Cross-Sectional Analyses of Over 100,000 Women in the Breakthrough Generations Study. American Journal of Epidemiology (2014) 10.1093/aje/kwu117