Falling asleep in front of the TV could increase the risk of obesity, new research suggests.
Women exposed to artificial light at night were more likely to gain weight and become obese or overweight over the next five years, according to a study of almost 44,000 people.
The findings, published in journal JAMA Internal Medicine, suggest that eliminating lights and screens from the bedroom could be another way to tackle the obesity crisis, the study authors said.
The researchers, from the National Institute of Environmental Health Sciences in the US, followed 43,722 women aged between 35 and 74 years old, over a period of at least five years.
The group provided information on their weight, body mass index (BMI), and any exposure to artificial light during the night.
Exposure to artificial light at night was linked with an increased risk of weight gain and the development of obesity, the study found.
Compared to those not exposed to artificial light, women who slept with a light or television on in the same room were 17 per cent more likely to gain 5kg or more over the next five years.
They were also 22pc more likely to become newly overweight and 33pc more likely to become newly obese.
"These results suggest that exposure to artificial light at night while sleeping may be a risk factor for weight gain and development of overweight or obesity," the authors said.
The researchers note that exposure to artificial light while sleeping might reflect other unhealthy behaviours, such as a sedentary lifestyle, and socioeconomic disadvantage.
However, commenting on the study, Professor Malcolm von Schantz, from the University of Surrey, said: "The findings make perfect biological sense.
"We know that light in the late evening will delay our body clocks.
"We know from experimental studies in people that light at night affects our metabolism in ways that are consistent with increased risk of metabolic syndrome.
"These new findings won't change the advice to maintain good sleep hygiene, and avoid light and electronic distractions in the bedroom, but they add further strength to the case for this advice."