Older women who leave the television and other lights on while asleep have a higher likelihood of becoming obese, according to a study published in JAMA Internal Medicine.

Researchers followed almost 44,000 women ages 35 to 74, some of whom were overweight, but not yet obese, according to self-reported body mass index scores. The women detailed their sleeping habits, noting what sources of artificial light they were regularly exposed to at night, and whether that source, such as a television or nightlight, was outside or inside the room. After six years, those who had lights on in the room were 22% more likely to report an overweight BMI, and 33% more likely to be obese than those who slept in complete darkness.

The results suggest that artificial light exposure at night should be addressed in obesity prevention discussions, said lead author Yong-Moon Park, Ph.D.