A new genetic study published in the journal, JAMA Psychiatry, on May 26 found that waking up one hour earlier can lower a person’s chance of major depression by 23%.
Researchers from the University of Colorado Boulder and the Broad Institute of MIT and Harvard studied 840,000 people and found some of the best evidence yet that chronotype, or a person’s proclivity to sleep at a specific hour, influences depression risk.
It’s also one of the first studies to measure how much, or how little, change is needed to have an impact on mental health. The results might have significant ramifications when individuals return to work and school remotely following the epidemic, a tendency that has pushed many to adjust to a later sleep pattern.
“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?” said senior author Celine Vetter, assistant professor of integrative physiology at CU Boulder. “We found that even one-hour earlier sleep timing is associated with significantly lower risk of depression.”
Past observational studies have found that night owls, regardless of how long they sleep, are twice as likely to suffer from depression as early risers. Researchers have had a difficult time figuring out what causes what since mood problems can impair sleep habits.
Other studies had limited sample numbers, relied on surveys from a single time point, or failed to account for environmental elements that might impact both sleep schedule and mood, thereby skewing the results.In 2018, Vetter released the results of a four-year study including 32,000 nurses, which found that “early risers” were up to 27% less likely to suffer depression.
Lead author Iyas Daghlas, M.D. used data from the DNA testing business 23 and Me and the biological database UK Biobank to figure out whether moving sleep time earlier is genuinely protective, and how big of a change is necessary. Daghlas then employed a technique known as “Mendelian randomization,” which relies on genetic correlations to help determine 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, who graduated in May from Harvard Medical School.
More than 340 common genetic variations are known to impact a person’s chronotype, including polymorphisms in the so-called “clock gene” PER2, and heredity accounts for 12-42 percent of our sleep time preference.
The researchers looked at deidentified genetic data on these variations from up to 850,000 people, including 85,000 people who wore wearable sleep trackers for seven days and 250,000 people who filled out sleep preference questionnaires. This provided them with a more detailed picture, down to the hour, of how genetic differences affect when we sleep and wake up.
In the largest of these samples, nearly a third of those polled identified as morning larks, 9% as night owls, and the remainder as somewhere in between. The average sleep mid-point was 3 a.m., indicating that they went to bed at 11 p.m. and awoke at 6 a.m. With this information, the researchers looked at a separate sample that contained genetic data, anonymized medical and medication records, and surveys on major depressive disorder diagnoses. They investigated whether persons with genetic variations that predispose them to be early risers also have a decreased risk of depression, using modern statistical tools. The answer is a resounding affirmative. A 23 percent decreased incidence of severe depressive illness was associated with each one-hour earlier sleep midpoint (halfway between bedtime and waking time).
This means that if someone who regularly goes to bed at 1 a.m. instead goes to bed at midnight and sleeps for the same amount of time, they can reduce their risk by 23%; if they go to bed at 11 p.m., they can reduce their risk by roughly 40%. According to the research, people who are already early risers may benefit from waking up even earlier. For those in the moderate or evening ranges, however, shifting to an earlier bedtime would likely be helpful.
What could be the cause of this phenomenon?
According to recent studies, obtaining more daylight during the day, as early risers do, triggers a chain reaction of hormonal changes that might affect mood. Others argue that having a biological clock, or circadian rhythm, that differs from the majority of people’s might be gloomy in and of itself.
“We live in a society that is designed for morning people, and evening people often feel as if they are in a constant state of misalignment with that societal clock,” said Daghlas.
“This study definitely shifts the weight of evidence toward supporting a causal effect of sleep timing on depression,” Daghlas added.
Dr. Vetter gives the following recommendations to individuals who desire to go on an earlier sleep schedule: “Keep your days bright and your nights dark,” she says. “Have your morning coffee on the porch. Walk or ride your bike to work if you can, and dim those electronics in the evening.”