A study of 1,788 adult twins is the first to demonstrate a gene by environment interaction between self-reported habitual sleep duration and depression symptoms. The study, “Sleep Duration and Depressive Symptoms: A Gene-Environment Interaction,” was published in the February 1 issue of the journal Sleep and suggests 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 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.

Another study, titled  “The Prospective Association between Sleep Deprivation and Depression among Adolescents,” consisted of 4,175 individuals between the ages of 11 and 17 years and documented reciprocal effects for major depression and short sleep duration among adolescents using prospective data. Results for this study are the first of its kind, and were also published in the February 1 issue of the journal Sleep. The findings reveal that sleeping six 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,” said principal investigator Robert E. Roberts, professor of behavioral sciences in the School of Public Health at the University of Texas Health Science Center in Houston, Texas. “Questions on sleep disturbance and hours of sleep should be part of the medical history of adolescents to ascertain risk.”

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