Studies find new links between sleep duration and depression

A genetic study of adult twins and a community-based study of adolescents both report novel links between sleep duration and depression. The studies are published in the Feb. 1 issue of the journal Sleep.

"Healthy sleep is a necessity for physical, mental and emotional well-being," said American Academy of Sleep Medicine President Dr. M. Safwan Badr. "This new research emphasizes that we can make an investment in our health by prioritizing sleep."

A study of 1,788 adult twins is the first to demonstrate a gene by environment interaction between self-reported habitual sleep duration and depressive symptoms. Results suggest that sleep durations outside the normal range increase the genetic risk for depressive symptoms. Among twins with a normal sleep duration of seven to 8.9 hours per night, the total heritability of depressive symptoms was 27 percent. However, the genetic influence on depressive symptoms increased to 53 percent among twins with a short sleep duration of five hours per night and 49 percent among those who reported sleeping 10 hours per night.

"We were surprised that the heritability of depressive symptoms in twins with very short sleep was nearly twice the heritability in twins sleeping normal amounts of time," said principal investigator Dr. Nathaniel Watson, associate professor of neurology and co-director of the University of Washington Medicine Sleep Center in Seattle, Wash.

"Both short and excessively long sleep durations appear to activate genes related to depressive symptoms," added Watson, who also serves on the board of directors of the American Academy of Sleep Medicine.

According to Watson, the study suggests that optimizing sleep may be one way to maximize the effectiveness of treatments for depression such as psychotherapy.

The relationship between sleep and depressive illness is complex – depression may cause sleep problems and sleep problems may cause or contribute to depressive disorders. For some people, symptoms of depression occur before the onset of sleep problems. For others, sleep problems appear first. Sleep problems and depression may also share risk factors and biological features and the two conditions may respond to some of the same treatment strategies. Sleep problems are also associated with more severe depressive illness.

Insomnia is very common among depressed patients. Evidence suggests that people with insomnia have a ten-fold risk of developing depression compared with those who sleep well. Depressed individuals may suffer from a range of insomnia symptoms, including difficulty falling asleep (sleep onset insomnia), difficulty staying asleep (sleep maintenance insomnia), unrefreshing sleep, and daytime sleepiness. However, research suggests that the risk of developing depression is highest among people with both sleep onset and sleep maintenance insomnia.