Both long and short sleep durations are associated with an increased heritability of depression, study findings show.
“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,” explains the team, led by Nathaniel Watson (University of Washington Medicine Sleep Center, Seattle, USA).
“These findings show a gene-environment interaction between sleep duration and depressive symptoms.”
Among 1788 adult twins, from 894 same-gender twin pairs, participating in the study, 66% reported a normal sleep duration of 7.0 to 8.9 hours, while 24% reported a short sleep duration of less than 7 hours and 9% a long sleep duration of 9 hours or more.
Sleep duration negatively correlated with self-reported depressive symptoms on the modified three-question Patient Health Questionnaire-9 (mPHQ-9), such that individuals with short or long sleep durations reported more depressive symptoms, on average, than individuals who slept for a normal length of time.
The correlation between sleep duration and depressive symptoms was seen within twin pairs. For example, the twin who reported the longer sleep duration had fewer depressive symptoms than the other twin and this effect was strongest for monozygotic relative to dizygotic twins. However, one twin’s sleep duration was not related to the other twin’s depressive symptoms.
This suggests that genetic influences on sleep duration do not account for the association between sleep duration and depressive symptoms, say the researchers in Sleep.
Sleep duration outside of the normal range increased the genetic risk for depressive symptoms. For individuals sleeping 8 hours per night, the total heritability of depressive symptoms was approximately 27%.
But among individuals sleeping just 5 hours a night, the heritability of depressive symptoms was 53% and it was 49% for those sleeping 10 hours a night.
The influence of sleep duration on depressive symptoms was down to shared genetic mechanisms; genes that overlap between sleep duration and depressive symptoms.
Based on recent research, the researchers suggest that “genes related to circadian rhythms, coupling of cell metabolism to electrical activity, and serotonergic neurotransmission may be central to the gene/environment interaction.”
They conclude: “This work suggests that environmentally mediated treatments for depression may have the greatest opportunity for success when administered in a patient sleeping normal amounts of time.
“Future research should consider the effects of habitual sleep duration on treatment success.”
This article first appeared on News Medical on 17 February, 2014.