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Light at Night Linked to Depression

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Not Enough Light

Many people are becoming aware of the fact that the lack of light in winter can cause seasonal depression known as SAD.

SAD is mainly due to the fluctuations in daylight hours as the seasons change, disrupting a person’s circadian rhythm—or internal clock—which controls a person’s physiological response to light and darkness.


Too Much Light?

Interestingly, recent LAN (light-at-night) research is suggesting that sleeping in a room with even a low level of light is associated with an increased risk of developing depression, even when the light did not cause people to awaken or experience other sleep disturbances during the night.

In the study, bedroom light intensity was measured objectively, and depressive symptoms were assessed. Of 863 participants (average age = 71.5 years) who did not have depressive symptoms at baseline, 73 participants reported the development of depressive symptoms during follow-up (median, 24 months).

The researchers found that people who were exposed to five lux* or more of light at night had a “significantly higher depression risk” than those who slept in darker rooms.

*Five lux is approximately the equivalent of the light that falls on a three-foot-square surface that is about three feet away from five candles.

Previous studies have suggested the possibility that LAN induces sleep disturbances, impaired melatonin secretion, and misalignments between sleep/wake behavior, and depression is frequently accompanied by these conditions.


Not Just Seniors

The researchers also point out that the association they found between LAN exposure and depressive symptoms is unlikely to be limited to older populations. In fact, quite the opposite may be true.

Age-related cloudiness of the crystalline lens causes decreased light reception to the retina, even before cataract diagnosis and the capacity for light reception of a 70-year-old is one-fifth of that of a teenager.



Research suggests that sleeping in total darkness may be a viable option to reduce the risk of depression.