Falling asleep with the TV on or having a bedroom that is illuminated by a street light at night could cause you to gain weight…

According to scientists at the National Institutes of Health, there is a link between any exposure to artificial light at night while sleeping and weight gain in women.

The research team used questionnaire data from 43 722 women in the Sister Study, a study that examined risk factors for breast cancer and other diseases.

Over 400 000 women studied

The study questionnaire asked participants (aged 35-74 years) whether they slept with no light, a small nightlight, light outside of the room, or a light or television on in the room.

The scientists used weight, height, waist and hip circumference, and body mass index measurements taken at baseline, as well as self-reported information on weight at baseline and follow-up five years later.

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Using this information, the scientists were able to study obesity and weight gain in women exposed to artificial light at night with women who reported sleeping in dark rooms.

Researchers found that using a small nightlight was not associated with weight gain, whereas women who slept with a light or television on were 17% more likely to have gained five kilograms or more over five years. The association with having light coming from outside the room was more modest.

Women who slept with a light or television on were 17% more likely to have gained five kilograms or more over five years

Light at night may alter hormones

The scientists wondered if not getting enough rest factored into the findings.

“Although poor sleep by itself was associated with obesity and weight gain, it did not explain the associations between exposure to artificial light while sleeping and weight,” says corresponding author Dale Sandler, Ph.D., chief of the Epidemiology Branch at the National Institute of Environmental Health Sciences (NIEHS), part of NIH.

“Humans are genetically adapted to a natural environment consisting of sunlight during the day and darkness at night. Exposure to artificial light at night may alter hormones and other biological processes in ways that raise the risk of health conditions like obesity,” says co-author Chandra Jackson, Ph.D., head of the NIEHS Social and Environmental Determinants of Health Equity Group.

Breast and prostate cancer linked to electronic blue light exposure at night

Source: NIH/National Institute of Environmental Health Sciences via www.sciencedaily.com

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