Waking up just an hour earlier every morning will help to reduce major depression in a person by 23 percent, a new genetic study published in the journal JAMA Psychiatry suggests.
Researchers from the University of Colorado Boulder and the Broad Institute of MIT and Harvard conducted a study on over 840,000 people and it shows some of the strongest evidence that chronotype, a person’s tendency to sleep at a certain time, influences depression risk.
The study which is also among the first to quantify just how much, or little, change is required to influence mental health is relevant in the post-pandemic period when people are working and attending school remotely and follow a rough sleep schedule.
“We have known for some time that there is a relationship between sleep timing and mood, but a question we often hear from clinicians is: How much earlier do we need to shift people to see a benefit? We found that even one-hour earlier sleep timing is associated with a significantly lower risk of depression,” said senior author Celine Vetter, assistant professor of integrative.
Previous observational studies have shown that night owl are as much as twice as likely to suffer from depression as early risers, regardless of how long they sleep. But because mood disorders themselves can disrupt sleep patterns, researchers have had a hard time finding out what causes what.
In 2018, Ms. Vetter published a large, long-term study of 32,000 nurses showing that “early risers” were up to 27 percent less likely to develop depression over the course of four years.
Genetic influence
To get a clearer sense of whether changing sleep time earlier is truly protective, and how much shift is required, lead author Iyas Daghlas, relied on data from the DNA testing company and used a method called “Mendelian randomization” that leverages genetic associations to help decipher cause and effect.
“Our genetics are set at birth so some of the biases that affect other kinds of epidemiological research tend not to affect genetic studies,” said Daghlas.
More than 340 common genetic variants, including variants in the so-called “clock gene” PER2, are known to influence a person’s chronotype, and genetics collectively explains 12 to 42 percent of our sleep timing preference.
The researchers examined de-identified genetic data on these variants from up to 850,000 individuals, including data from 85,000 who had worn wearable sleep trackers for 7 days and 250,000 who had filled out sleep-preference questionnaires. This gave them a more clear picture, down to the hour, of how variants in genes influence when we sleep and wake up.
In the largest of these samples, about a third of surveyed subjects self-identified as morning larks, 9 percent were night owls and the rest were in the middle. Overall, the average sleep mid-point was 3 a.m., meaning they went to bed at 11 p.m. and got up at 6 a.m.
With this information in hand, the researchers turned to a different sample which included genetic information along with anonymized medical and prescription records and surveys about diagnoses of major depressive disorder.
Using novel statistical techniques, the researchers asked: Do those with genetic variants which predispose them to be early risers also have a lower risk of depression? The answer is a firm yes. Each one-hour earlier sleep midpoint (halfway between bedtime and wake time) corresponded with a 23 percent lower risk of major depressive disorder.
This suggests that if someone who normally sleeps at 1 a.m. goes to bed at midnight instead and sleeps the same duration, they could cut their risk by 23 percent; if they go to bed at 11 p.m, they could cut it by about 40 percent.
It’s unclear from the study whether those who are already early risers could benefit from getting up even earlier. But for those in the intermediate range or evening range, shifting to an earlier bedtime would likely be helpful.
Some research suggests that getting greater light exposure during the day, which early-risers tend to get, results in a cascade of hormonal impacts that can influence mood. Others note that having a biological clock, or circadian rhythm, that trends differently than most peoples’ can in itself be depressing.
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