The amount of shut-eye you get each night could affect your risk for depression, new research suggests.
Two studies, both published in the journal Sleep, show links between depression and getting too much and too little sleep in adults, as well as a link between depression and too little sleep in adolescents.
While there is no blanket recommendation for the amount of sleep adults should get each night, most adults need seven to nine hours to feel rested, according to the National Sleep Foundation. Meanwhile, teens generally need between 8.5 and 9.25 hours of sleep a night.
The first study, conducted by researchers at the University of Washington, University of Pennsylvania and the University of Texas at Austin, was conducted in 1,788 same-sex adult twin pairs, who were part of the University of Washington Twin Registry. All of the participants reported their typical sleep duration, as well as any symptoms of depression.
Generally, researchers found that people in the study who slept a "normal" amount each night -- between seven and 8.9 hours a night -- had a 27 percent heritability of depressive symptoms. But people who slept fewer than seven hours a night or nine or more hours a night had an increased heritability of depressive symptoms: 53 percent for the short sleepers and 49 percent for the long sleepers.
"As sleep duration moved away from the extremes and toward the 'normal' range, the effect of the non-shared environment was more strongly associated with depressive symptoms, while genetic factors became less important," the researchers wrote in the study. "These findings show a gene-environment interaction between sleep duration and depressive symptoms."
The researchers noted that while the study did not explain specifically how genetic factors explained the link, "recent findings suggest candidate genes and pathways."
The other study, conducted by researchers from the University of Texas Health Science Center and the Centers for Disease Control in Vietnam, examined sleep duration and depression risk for adolescents. For the study, 4,175 Houston-area 11-to-17-year-olds had their sleep and depression symptoms measured.
Researchers found that sleep deprivation was predictive of depression. Specifically, getting six or fewer hours of sleep a night (including weekends) was associated with increased risk of depression. They did not, however, find that depressive symptoms predicted the sleep deprivation.
"These results, particularly for major depression, suggest that quantity of sleep, following DSM-IV guidelines increases risk for major depression, which in turn increases risk for decreased sleep," the researchers wrote in the study. "This is not surprising, given the phenomenology of both sleep disturbances and major depression."