Sleeping in a room with too much light may increase the risk of weight gain and obesity, according to a study published in the American Journal of Epidemiology. Researchers from the Institute of Cancer Research in London found that women whose bedrooms were ‘light enough to see across’ at night, had larger waistlines than those who slept in darker rooms. While the reason behind the link is unknown, the researchers speculate that exposure to artificial light may alter the way food is digested in a 24-hour cycle.

“There is an association between reported light exposure at night and overweight and obesity,” said lead author Professor Anthony Swerdlow, “but there is not sufficient evidence to know if making your room darker would make any difference to your weight.”