Study says even a little light at night could contribute to depression


Many people can’t stand to have even a little light in their room when they are falling asleep, but a new study shows it might be more than just an annoyance. According to findings published in the American Journal of Epidemiology, low-level nighttime light exposure may be linked to depression in older adults.

The study, co-authored by Kenji Obayashi, a professor in community health and epidemiology at the Nara Medical University School of Medicine in Japan, indicates that sleeping in anything but total darkness could have a negative impact on mental health – especially at higher ages.

“Maintaining darkness in the bedroom at night may be a novel and viable option to prevent depression,” Obayashi told TIME via email.

For the study, the team measured the levels of nighttime light in the bedrooms of 863 elderly Japanese adults using ceiling-facing light meters at the heads of the participant’s beds for two nights. This gave an approximate measure of their typical nighttime light exposure.

The participants also completed detailed sleep diaries and filled out surveys measuring depression symptoms for two years.

Of the 863 participants, 73 developed signs of depression during the two-year follow-up period. When evaluated for their light exposure, the team found a correlation between their depression progression and the amount of nighttime light present in their bedrooms.

Specifically, those who were exposed to more than five lux of light at night were significantly more likely to develop symptoms of depression compared to those who slept in a completely dark room.

The researchers note the study is limited and can’t prove a cause-and-effect relationship. There were likely other factors involved that could have contributed to the development of depression, but Obayashi and colleagues say the findings show nighttime light exposure can have a notable role on mental health. Obayashi suggests light could be related to sleep disturbances would could throw off the sleep patterns of a person, impairing the production of melatonin or other hormones created during sleep.

The study co-author also believes the effects could be more pronounced among younger individuals, though this version of the study did not include them. “The capacity for light reception of a 70-year-old is one-fifth of that of a teenager,” he says.

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