If you like to sleep with a tiny night-lamp glowing in the darkness, you might want to reconsider it. A group of behavioural scientists working on hamsters have found that exposure to dim light at night can lead to depression. In fact, increasing prevalence of artificial light at night is seen as a possible link to increasing rates of depression. However, experiments also reveal that this is reversible by merely restoring complete darkness during sleep over a period of time.

Biological Implications of Lights at Night

Chronic exposure to artificial light at night is termed as a health hazard important enough to be given an abbreviation— LAN. There is increasing evidence that it may influence the onset of breast cancer, heart disease and obesity. Unnatural lighting at night is now widespread, and could affect the body’s circadian clock, disruptions of which have been linked to depressive disorders.

Researchers at Ohio State University used two groups of hamsters in their experiments. The first group was allowed to sleep in complete darkness, while animals of the second group slept in an area illuminated by a dim light. The second group of animals showed decreased physical activity and depressive symptoms, including a decreased tendency to consume sugary water, an anhedonic response. Upon removal of the LAN for this group for two weeks, the depressive symptoms disappeared, showing that LAN has a reversible effect on mood.

Why We Must Embrace the Darkness

Why would light at night lead to mood disorders? Our body responds to light by suppressing the secretion of a hormone called melatonin. What is ‘night-time’ for our body depends on whether melatonin is secreted or not. Even dim light (the light used in this experiment was of intensity 5 lux) is sufficient to suppress melatonin, which meddles with the body’s internal timing. In fact, melatonin has been linked to mood disorders, and molecules which react with melatonin are used as antidepressants.

This study should throw up important questions in the face of increasing light pollution around the world. Perhaps it is time for the Dark Night to rise again.

You can read about this research here.