WASHINGTON (Reuters) – Women who sleep on television or turn on a light in their bedroom may be more likely to gain weight, according to a new study.
The research, published in the Journal of the American Medical Association (JAMA) of Internal Medicine, featured a survey of nearly 44,000 American women, followed up five years later.
Women were classified according to their level of exposure to artificial light at night (ALAN), which came from a variety of sources, from small night lights or radios-clocks to street lights, televisions or split lights.
One of the key findings was that women who slept on television or turned on the light in the room were 17 percent more likely to gain five pounds or more during the study period.
The correlation remained strong even after controlling for factors such as sleep duration, diet and physical activity.
Although the authors warned that they could not establish a causal link, they said their findings were added to a growing body of evidence supporting sleep in a dark room.
"Public health strategies to reduce obesity may consider interventions that aim to reduce ALAN during sleep," wrote Dale Sandler and Yong-Moon Mark Park of the National Institute of Environmental Health Sciences of North Carolina and co-authors.
They suggested that light may be suppressing the production of melatonin, thus interrupting the circadian rhythm and eating patterns.
Other possibilities were that light acts as a "chronic stressor," disrupting the release of stress hormones, such as glucocorticoids, that play a role in regulating food intake, or that there may be another mechanism that directly affects metabolism.
The authors recognized several limitations, including that the data were self-reported and did not know how intense the various light sources were.
High light exposure may also "reflect a constellation of measures of socioeconomic disadvantage and unhealthy lifestyle behaviors that may contribute to weight gain and obesity."
Commenting on the paper, Malcolm von Schantz, a professor of chronobiology at the University of Surrey in Britain, said: "What is new in this article is that it is a longitudinal study comparing the weight of the same subjects at the start of the study and more five years later. "
He added, "These new findings will not change advice to maintain good sleep hygiene and avoid light and electronic distractions in the bedroom, but add strength to the case for this advice."