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Waking up just one hour earlier could reduce a person's risk of major depression by 23%, suggests a sweeping new genetic study published May 26 in the journal JAMA Psychiatry.

The study of 840,000 people, by researchers at University of Colorado Boulder and the Broad Institute of MIT and Harvard, represents some of the strongest evidence yet that chronotype -- a person's propensity to sleep at a certain time -- influences depression risk.


As people emerge, post-pandemic, from working and attending school remotely -- a trend that has led many to shift to a later sleep schedule -- the findings could have important implications.

"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."


Other studies have had small sample sizes, relied on questionnaires from a single time point, or didn't account for environmental factors which can influence both sleep timing and mood, potentially confounding results.

In 2018, Vetter published a large, long term study of 32,000 nurses showing that "early risers" were up to 27% less likely to develop depression over the course of four years, but that begged the question: What does it mean to be an early riser?

To get a clearer sense of whether shifting sleep time earlier is truly protective, and how much shift is required, lead author Iyas Daghlas, M.D., turned to data from the DNA testing company 23 and Me and the biomedical database UK Biobank. Daghlas then 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, who graduated in May from Harvard Medical School.

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 12-42% of our sleep timing preference.





The answer is a firm yes.




What could explain this effect?


Others note that having a biological clock, or circadian rhythm, that trends differently than most peoples' can in itself be depressing.

"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.

He stresses that a large randomized clinical trial is necessary to determine definitively whether going to bed early can reduce depression. "But this study definitely shifts the weight of evidence toward supporting a causal effect of sleep timing on depression."


"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."

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