It may be time to invest in some blackout curtains, according to new research.

A study published recently in the American Journal of Epidemiology found a strong association between even low-level nighttime light exposure and depressive symptoms among elderly adults.

The researchers measured nighttime light levels in the bedrooms of 863 elderly Japanese adults by placing ceiling-facing light meters at the heads of everyone’s beds for two nights. The people in the study also completed sleep diaries and were monitored through surveys for the development of depression symptoms over the course of two years.

Seventy-three people developed depressive symptoms during the follow-up period, and the researchers found a correlation between that progression and exposure to nighttime light. People who saw more than five lux of light at night were much more likely to develop symptoms of depression than those who slept in a completely dark room.

And while the study focused specifically on elderly adults, the effects may be even more pronounced among younger people, whose eyes are more sensitive and thus register more light. “The capacity for light reception of a 70-year-old is one-fifth of that of a teenager,” so it’s probably a good idea to shut out as many sources of light as possible when you sleep, no matter your age.

– Jamie Ducharme

Read more: Being Exposed to Light During Sleep Linked to Depression

Image by Gregory Pappas from Unsplash