The common bedroom mistake that could cause you to gain weight

While weight gain has been linked to everything from fatty foods to a lack of exercise, researchers now believe a common bedroom habit could also be a major risk factor for developing obesity.

Many people find that it’s easier to doze off with the TV on when they go to bed, but researchers from the National Institute of Health have, for the first time, found an association between exposure to artificial light while sleeping and weight gain.

The study, published in the JAMA Internal Medicine Journal, focused specifically on women and claimed that cutting off artificial lights at bedtime could reduce the chance of becoming obese. Researchers used questionnaire data from 43,722 women in a cohort study that examined risk factors for breast cancer and other disease.

The women were aged between 35 and 74 and were asked how much light they were exposed to when they slept. Their options were no light, a small nightlight, light outside the bedroom or a light or television in the room.

Scientists were able to study weight gain and obesity in women exposed to artificial light in a follow-up study five years later by analysing the women’s responses to the questionnaire and by using information about their weight, height, waist and hip circumference and body mass index measurements.

The study found weight gain varied and depended on the level of artificial light women were exposed to. A small nightlight wasn’t associated with weight gain, but those who slept with a light on or with a television playing were 17 per cent more likely to have gained five kilograms more over the follow-up-period.

Researchers questioned whether not getting enough sleep was a contributing factor to the weight gain.

Read more: From pneumonia to gum disease: The dangers of sleeping in unwashed sheets

“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,” corresponding author Dale Sandler said in a statement.

The authors also questioned the impact living in urban environments played in weight gain, noting streetlights, store front neon signs and other light sources are more common in these areas. These light sources can suppress the sleep hormone melatonin, researchers claimed.

“Humans are genetically adapted to a natural environment consisting of sunlight during the day and darkness at night,” study co-author Chandra Jackson said. “Exposure to artificial light at night may alter hormones and other biological processes in ways that raise the risk of health conditions like obesity.”

While the study acknowledged that other confounding factors may explain the associations between artificial light and weight gain, the results didn’t change when factors such as age, calories consumed and physical activity were taken into account.

“Unhealthy high-calorie diet and sedentary behaviours have been the most commonly cited factors to explain the continuing rise in obesity,” lead author Yong-Moon Park said. “This study highlights the importance of artificial light at night and gives women who sleep with lights or the television on a way to improve their health.”

Read more: Why a better sleep makes for healthier ageing

It’s always important to talk to a health professional about the best ways to maintain a healthy weight.

Do you sleep with your TV on? Do you think this could contribute to weight gain?