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Otautahi – Waking up just one hour earlier could reduce a person’s risk of major depression by 23 percent, suggests a new US genetic study has found.

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 a person’s propensity to sleep at a certain time influences depression risk.

It’s also among the first study 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 may have important implications.

Researchers have known for some time that there is a relationship between sleep timing and mood.

They found even one-hour earlier sleep timing is associated with significantly lower risk of depression. The study is published in the JAMA psychiatry journal.

Previous 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.

An earlier study of 32,000 nurses showed early risers were up to 27 percent 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, the researchers turned to data from DNA biomedical database companies for help.

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 the samples, about a third of surveyed subjects self-identified as morning larks, nine percent were night owls, and the rest were in the middle.

Findings suggested that if someone who normally goes to bed at 1 am goes to bed at midnight instead and sleeps the same duration, they could cut their risk of depression by 23 percent. If they went to bed at 11 pm, they could cut it by about 40 percent.