Waking just one hour earlier cuts depression risk by double digits, study finds
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.
It’s also among the first studies to quantify just how much, or little,
change is required to influence mental health.
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.”
Previous observational studies have shown that night owls 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 deciphering what causes what.
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 researchers assessed deidentified 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 granular 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% 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, they asked: Do those with genetic
variants which predispose them to be early risers also have 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% lower risk of major depressive disorder.
This suggests that if someone who normally goes to bed at 1 a.m. goes to
bed at midnight instead and sleeps the same duration, they could cut their risk
by 23%; if they go to bed at 11 p.m., they could cut it by about 40%.
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.
What could explain this effect?
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.
“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.”
For those wanting to shift themselves to an earlier sleep schedule,
Vetter offers this advice:
“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.”
Journal Reference:
- Iyas Daghlas,
Jacqueline M. Lane, Richa Saxena, Céline Vetter. Genetically Proxied
Diurnal Preference, Sleep Timing, and Risk of Major Depressive Disorder. JAMA
Psychiatry, 2021; DOI: 10.1001/jamapsychiatry.2021.0959