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 February 1 issue of the journal Sleep.

“Healthy sleep is a necessity for physical, mental, and emotional well-being,” says American Academy of Sleep Medicine (AASM) President Dr M. Safwan Badr, in a release. “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 7 to 8.9 hours per night, the total heritability of depressive symptoms was 27%. However, the genetic influence on depressive symptoms increased to 53% among twins with a short sleep duration of 5 hours per night and 49% 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,” says principal investigator Dr Nathaniel Watson, associate professor of neurology and co-director of the University of Washington Medicine Sleep Center in Seattle. “Both short and excessively long sleep durations appear to activate genes related to depressive symptoms,” adds Watson, who also serves on the AASM board of directors.

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

Another study of 4,175 individuals between 11 and 17 years of age is the first to document reciprocal effects for major depression and short sleep duration among adolescents using prospective data. Results suggest sleeping 6 hours or less per night increases the risk for major depression, which in turn increases the risk for decreased sleep among adolescents.

“These results are important because they suggest that sleep deprivation may be a precursor for major depression in adolescents, occurring before other symptoms of major depression and additional mood disorders,” says principal investigator Dr Robert E. Roberts, professor of behavioral sciences in the School of Public Health at the University of Texas Health Science Center in Houston. “Questions on sleep disturbance and hours of sleep should be part of the medical history of adolescents to ascertain risk.”