Depression affects many aspects of life, and for some people it may mean that they sleep longer or different hours than they would normally. “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?” says senior author Celine Vetter, assistant professor of integrative physiology at Colorado University Boulder, in a press release.
A previous study from Vetter and collaborators found that in a four-year study of 32,000 nurses that “early risers” were 27 percent less likely to develop depression symptoms. But how would shifting a sleep schedule potentially affect people? That’s what this new study focuses on.
The study followed 840,000 people and collected data on their chronotype, meaning what hours of the day they were predisposed to prefer, based on genetic information. One “clock gene” is thought to account for 12 to 42 percent of our sleep timing.
The researchers wanted to know if someone’s genetics makes them more likely to be an “early riser” if they also have lower risk for depression. So they gave some study participants sleep trackers and some filled out a sleep preference questionnaire. They then connected those data to genetic data.
The team focused on the sleep midpoint, calculated as halfway between bedtime and wake time. “We found that even one-hour earlier sleep timing is associated with significantly lower risk of depression,” says Vetter in the press release. So if someone who normally goes to bed at midnight instead goes to bed at 11 PM and sleeps for the same duration, they could cut their risk by 23 percent, according to the study. The effect could be nearly twice that if shifted by two hours.
The researchers aren’t certain why they are seeing these results, but it may have to do with light and darkness and how our bodies react. Light research has shown that light therapy can be helpful for treating some mood disorders.
The connection to depression symptoms could also be a result of societal norms. Simply having a chronotype that does not make you an early riser could be having an effect. “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,” says lead author Iyas Daghlas at the Broad Institute of MIT and Harvard.
If you want to shift to an earlier sleep schedule, there are some things you can do to help make that process easier. “Keep your days bright and your nights dark,” says Vetter. “Have your morning coffee on the porch. Walk or ride your bike to work if you can, and dim those electronics in the evening.”