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Women who are exposed to greater levels of light while sleeping are more likely to gain weight, a new study has claimed.
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 study of 113,000 women was published in the American Journal of Epidemiology and was sponsored by the charity Breakthrough Breast Cancer. The findings emerged from a long-term study to understand the risk factors for breast cancer.
The women were asked to rate the amount of light in their bedrooms at night as:
Light enough to read
Light enough to see across the room, but not read
Light enough to see your hand in front of you, but not across the room
Too dark to see your hand or you wear a mask
Their answers were compared to measures of Body Mass Index, waist-to-hip ratio and waist circumference which were all higher in women with lighter rooms.
Prof Anthony Swerdlow, from the Institute of Cancer Research, told the BBC: “In this very large group of people there is an association between reported light exposure at night and overweight and obesity.
“But there is not sufficient evidence to know if making your room darker would make any difference to your weight.
“There might be other explanations for the association, but the findings are intriguing enough to warrant further scientific investigation.”
One possible explanation is that the light is disrupting the body clock, which stems from our evolutionary past when we were active when it was light in the day and resting when it was dark at night.
Light alters mood, physical strength and even the way we process food in a 24-hour cycle.
Artificial light is known to disrupt the body clock by delaying the production of the sleep hormone melatonin.
Dr Matthew Lam, from Breakthrough Breast Cancer, commented: “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.”
Agencies/Canadajournal
