A study from CU Boulder is shedding new light on the link between sleep timing and mental health. The experts report that waking up just one hour earlier could reduce a person’s risk of major depression by 23 percent.
In collaboration with researchers at the Broad Institute of MIT and Harvard, the team has uncovered some of the strongest evidence yet that chronotype – a person’s propensity to sleep at a certain time – influences depression risk.
The investigation, which was focused on 840,000 people, is among the first of its kind to quantify just how much, or little, change is required to influence mental health.
The findings could have important implications as many people emerge from the COVID-19 pandemic with later sleep schedules.
“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 study senior author Professor Celine Vetter. “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 up to twice as likely to suffer from depression as early risers, regardless of sleep duration. However, considering that mood disorders can disrupt sleep patterns, it is difficult to establish which is the cause and which is the effect.
In 2018, Vetter conducted a long term study of 32,000 nurses which established that “early risers” were up to 27 percent less likely to develop depression over the course of four years. This research prompted the question – what does it mean to be an early riser?
To investigate whether an earlier sleep time is truly protective, as well as how big of a shift is required, study lead author Dr. Iyas Daghlas used data from the DNA testing company 23 and Me and the biomedical database UK Biobank. He applied a method called “Mendelian randomization” 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 Dr. Daghlas.
An individual’s chronotype is influenced by more than 340 common genetic variants, including variants in the so-called “clock gene” PER2. As much as 42 percent of our sleep timing preference can be attributed to genetics.
The researchers analyzed genetic data on these variants from up to 850,000 individuals, many of whom had worn wearable sleep trackers for 7 days or filled out sleep-preference questionnaires. This helped to show – down to the hour – how variants in genes influence when we sleep and wake up.
About one third of the participants who were surveyed self-identified as morning larks, 9 percent as night owls, and the rest were in the middle. Overall, the average sleep timing was from 11 p.m. to 6 a.m.
Next, the researchers turned to a different sample which included genetic information along with medical records and surveys about major depressive disorder. They found clear evidence that people with genetic variants which predispose them to be early risers also have lower risk of depression.
For each one-hour earlier sleep midpoint, which is halfway between bedtime and wake time, there was a corresponding with a 23 percent lower risk of major depressive disorder. In other words, if someone who normally goes to bed at 1 a.m. goes to bed at midnight and sleeps the same duration, they could cut their risk by 23 percent. Furthermore, if the individual went to bed at 11 p.m., they could cut the risk of depression by about 40 percent.
One explanation for the results could be greater light exposure during the day, which leads to a cascade of hormonal impacts that can influence mood.
“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 emphasized that a large randomized clinical trial is needed to confirm that going to bed early can reduce depression.
“Keep your days bright and your nights dark. Have your morning coffee on the porch,” said Vetter. “Walk or ride your bike to work if you can, and dim those electronics in the evening.”
The study is published in the journal JAMA Psychiatry.