Date: May 28, 2021

Source: University of Colorado at Boulder

Summary:

A genetic study of 840,000 people found that changing bedtimes just an hour earlier reduced the risk of major depression by 23%.

Waking up an hour earlier can reduce a person’s risk of major depression by 23%, a new genetic study published May 26 in the journal JAMA Psychiatry suggests.

The study of 840,000 people, by researchers at the University of Colorado Boulder and the Broad Institute of MIT and Harvard, represents some of the strongest evidence yet for timing — a person’s tendency to fall asleep at a time certain – affects the risk of depression.

It is also one of the first studies to quantify how much change is needed to affect mental health.

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

“We’ve known for a long time that there’s a relationship between sleep duration and mood, but one question we often hear from doctors is: How much sooner do we need to change people to see benefits? useful?” said senior author Celine Vetter, assistant professor of integrative physiology at CU Boulder. “We found that an hour earlier in sleep was even associated with a significantly lower risk of depression.”

Previous observational studies have shown that night owls are twice as likely to suffer from depression as early risers, regardless of how long they sleep. But because mood disorders themselves can also disrupt sleep, researchers have had trouble deciphering which triggers which.

Other studies were small, based on questionnaires from a single time point, or did not account for environmental factors that can affect both sleep duration and mood, potentially confounding the results. .

In 2018, Vetter published a large, long-term study of 32,000 nurses that found that “early risers” were up to 27% less likely to develop depression over the course of 4 years, but that puts Question: What does it mean to be an early riser?

Lead author Iyas Daghlas, MD, turned to data from DNA testing company 23 and Me and the UK biomedical database UK Biobank to gain insight into whether altering sleep time earlier actually has an effect. useful or not. Daghlas then used a method called “Mendelian randomization” that leverages genetic links to help decipher cause and effect.

“Our genetics research was set at birth, so some biases that affect other types of epidemiological studies have been found,” said Daghlas, who graduated from Harvard Medical School in May. trend does not affect genetic studies”.

More than 340 common genetic variants, including those in the so-called “clock gene” PER2, are known to affect a person’s time pattern, and genetics collectively explain 12-42% of preferences about our sleep time.

The researchers evaluated genetic data identified on these variants from up to 850,000 individuals, including data from 85,000 people who wore a wearable sleep tracker for 7 days and 250,000 who filled out a questionnaire about sleep preferences. This gave them a more detailed, hour-by-hour picture of how variations in genes affect when we sleep and wake up.

In the largest sample of these, about a third of the subjects surveyed identified themselves as morning crested birds, 9% as night owls and the rest in between. Overall, the average sleep midpoint was 3 a.m., meaning they went to bed at 11 p.m. and woke up at 6 a.m.

With this information in hand, the researchers turned to another sample that included genetic information along with anonymous medical records and prescriptions and a survey of diagnoses of major depressive disorder.

Using new statistical techniques, they asked: Do people with genetic variants that make them early risers also have a lower risk of depression?

The answer is definitely yes.

Each midpoint of sleep an hour earlier (between bedtime and waking) corresponds to a 23% reduction in the risk of major depressive disorder.

This suggests that if someone normally goes to bed at 1 a.m. instead goes to bed at midnight and sleeps at the same time, they can reduce their risk of disease by 23%; if they go to bed at 11 p.m., they can cut about 40%.

Research is still unclear whether people who are already up early can benefit from waking up earlier. But for those who are in the middle or around the evening, switching to an earlier bedtime can be helpful.

What could explain this effect?

Some research suggests that greater light exposure during the day, which early risers tend to suffer from, leads to a range of hormonal effects that can affect mood.

Others note that having a circadian clock, or circadian rhythm, that tends to be different for most people, in itself can be depressing.

“We live in a society designed for people who, in the morning, and in the evening often feel as if they are always off-balance with that social clock,” says Daghlas.

He stressed that a large randomized clinical trial is needed to definitively determine whether going to bed early can reduce depression. “But this study certainly shifts the weight of evidence to support a causal effect of sleep duration on depression.”

For those looking to switch to an earlier bedtime schedule, Vetter offers the following advice:

“Keep your day bright and your nights dark,” she says. “Have your morning coffee on the porch. Walk or cycle to work if you can and limit electronic devices in the evening.”

Source: Materials provided by University of Colorado at Boulder. Original written by Lisa Marshall.

References:

Iyas Daghlas, Jacqueline M. Lane, Richa Saxena, Celine Vetter. Genetically Proxied Diurnal Preference, Sleep Timing, and Risk of Major Depressive Disorder. JAMA Psychiatry, 2021; DOI: 10.1001/jamapsychiatry.2021.0959

University of Colorado at Boulder. “Waking just one hour earlier cuts depression risk by double digits, study finds.” ScienceDaily. ScienceDaily, May 28, 2021. .

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