Light During Sleep in Older Adults Linked to Metabolic Disease

In a sample of older men and women ages 63 to 84, those who were exposed to any amount of light while sleeping at night were significantly more likely to be obese, and have high blood pressure and diabetes compared to adults who were not exposed to any light during the night, reports a new Northwestern Medicine study in the journal SLEEP.

Light exposure was measured with a wrist-worn device and tracked over seven days.  

“Whether it be from one’s smartphone, leaving a TV on overnight or light pollution in a big city, we live among an abundant number amount of artificial sources of light that are available 24 hours of a day,” says study corresponding author Minjee Kim, MD, assistant professor of neurology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician, in a statement. “Older adults already are at higher risk for diabetes and cardiovascular disease, so we wanted to see if there was a difference in frequencies of these diseases related to light exposure at night.”    

Study investigators were surprised to find that less than half of the 552 study participants consistently had a five-hour period of complete darkness per day. The rest of the participants were exposed to some light even during their darkest five-hour periods of the day, which were usually in the middle of their sleep at night. 

Because this was a cross-sectional study, investigators don’t know if obesity, diabetes and hypertension cause people to sleep with a light on, or if the light contributed to the development of these conditions. Individuals with these conditions may be more likely to use the bathroom in the middle of the night (with the light on) or may have another reason to keep the light on. Someone with foot numbness because of diabetes may want to keep a night light on to reduce the risk of falls. 

“It’s important for people to avoid or minimize the amount of light exposure during sleep,” says senior study co-author Phyllis Zee, MD, chief of sleep medicine at Feinberg and a Northwestern Medicine physician, in a statement.