According to this NIH study, light exposure at night might contribute to weight gain and obesity in women independently of calories consumed, physical activity and sleep length and quality. Women were followed up for more than 5 years and those who slept with a light or television on were more likely to gain weight and develop obesity compared with those who were not exposed to artificial light. This study “suggests that lowering exposure to artificial light while sleeping might be a useful intervention for obesity prevention”.
Women who slept with a television or light on were more likely to gain weight and develop obesity. The findings suggest that turning off lights at bedtime could help keep off extra pounds.