Research has found that major depression risk can be reduced by as much as 23% by waking up 1 hour earlier. The study consisted of 840,000 individuals, and the results offer strong evidence that chronotype, which is an individual’s tendency to sleep at a particular time, can influence the risk of depression. The results also indicate the amount of change that’s required for influencing mental health.1✅ JOURNAL REFERENCE
Prior research has found night owls are nearly two times as likely to experience depression compared to early risers, irrespective of the amount of time they have slept. But due to the fact mood disorders on their own can affect sleep patterns, there has been some difficulty in figuring out what is causing what.
Other research has had modest sample sizes, depended on questionnaires from a single point in time, or did not consider environmental factors that can have an effect on both timing of sleep and mood, which potentially confuses the results.
A 2018 long term study of 32,000 participants demonstrated that “early risers” were nearly 27% more unlikely to have depression during a period of 4 years, but did not explain exactly what it means to be an early riser.
To get a better picture of whether changing sleep time is really protective, and how much change is needed, a method referred to as “Mendelian randomization” was made use which utilizes genetic associations to help make sense of expected outcomes.
Over 340 typical genetic variants, which include variants in the PER2 gene known as the “clock gene”, are known to have an impact on an individual's chronotype, and genetics explains 12% to 42% of sleep timing preferences.
Genetic data was examined on these variants from as many as 850,000 people, which included data from 85,000 individuals who had for 7 days donned wearable sleep trackers and 250,000 individuals who had completed questionnaires related to their sleep preferences. This presented the researchers with a more granular representation, precisely to the hour, of just how variants in genes impact our sleeping and waking up times.
In the biggest of these samples, approximately a third of the individuals surveyed self-identified as early risers, 9% as night owls and the remainder were in between. The average sleep mid-point overall was 3 a.m., which means the individuals went to sleep at 11 p.m. and woke up at 6 a.m.
With this data available, a different sample was examined which incorporated genetic information together with anonymized prescription and medical records as well as surveys about major depressive disorder diagnoses.
Making use of novel statistical methods, it was determined that individuals having genetic variants that predispose them to wake up earlier also have a reduced risk of depression.
Each sleep midpoint of 1 hour (halfway point between sleeping and waking time) was associated with a 23% depression risk reduction.
This indicates that if an individual who usually goes to sleep at 1 a.m. goes to sleep at midnight instead and is sleeping the same length of time, depression risk could be cut by 23%; if they go to sleep at 11 p.m., risk could be cut by about 40%.
It's not clear from the study if early riser individuals could benefit from waking up even earlier. For individuals in the intermediate or evening range, changing to an earlier sleep time would probably be helpful.
Some research indicates that early-risers are likely to get more exposure to light for the duration of the day, which causes a cascade of hormonal influencing factors that can help impact mood.
Other research suggests that having a biological clock that trends in a different way compared with most individuals' can be depressing in itself.
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