Good sleep habits are important for maintaining good physical and mental health. Epidemiological studies have revealed a decreased risk of major depressive disorder in those who prefer to wake up early and go to sleep early. Authors of a report recently released studied the genetic associations between early sleep/wake preference and depression.

Depression is a disease with multiple contributing factors that include environmental, lifestyle, and genetic influences. Untangling the web of factors contributing to late sleep preference and depression risk may help identify interventions to treat depression.

Earlier sleep and wake times align better with typical work and social schedules, increase daily light exposure, and enhance sensitivity to rhythmic changes in brain activity, contributing to a lower risk of depression. While environmental and social factors may dictate a person’s wake and sleep schedule, genetic factors may also play a role in sleep timing preferences.

The authors performed a genome-wide association study, which is an observational study where researchers look for associations between gene variations called single-nucleotide polymorphisms and disease prevalence. The authors collected genetic data and depression status from over 500,000 participants in the Psychiatric Genomics Consortium and United Kingdom Biobank studies to determine genetic proxies for depression. They also collected genetic and sleep data from over 700,000 participants in the United Kingdom Biobank and 23andMe research studies to determine genetic proxies for sleep time preference. Some participants wore an activity monitor to measure their sleep precisely. The researchers calculated the sleep midpoint (halfway between falling asleep and waking) and used this in their model of genetic data as well.

Participants with an earlier sleep preference were 23 percent less likely to have depression. This decreased risk was additive for every hour that the midpoint of sleep occurred earlier in the night. That means shifting sleep one hour earlier at night and waking one hour earlier in the morning may decrease depression risk, but shifting the sleep window even earlier may decrease risk even more. The relationship between early or late waking preference and depression was significant for both physician-diagnosed and self-reported depression.

The authors concluded that the association between genetics, sleep, and depression revealed by their study provides support for sleep interventions in patients with depression.

• Link to full report.
• Learn more about circadian clocks and their importance in health in this clip featuring Dr. Satchin Panda.