Early to bed, early to rise may make women less prone to depression.
That’s the takeaway from one of the largest studies yet to explore the link between chronotype, or sleep-wake preference, and mood disorders.
For the study, published this week in the Journal of Psychiatric Research, researchers at CU Boulder and the Channing Division of Network Medicine at Brigham and Women’s Hospital looked at data from more than 32,000 female nurses.
They found that even after accounting for environmental factors like light exposure and work schedules, chronotype—which is in part determined by genetics—appears to mildly influence depression risk.
“This could be related to the overlap in genetic pathways associated with chronotype and mood,” said lead author Céline Vetter, director of the Circadian and Sleep Epidemiology Laboratory (CASEL) at CU Boulder.
Previous studies have shown that night owls are as much as twice as likely to suffer from depression. But because those studies often used data at a single time-point and didn’t account for many other factors that influence depression risk, it has been hard to determine whether depression leads people to stay up later or a late chronotype boosts risk of depression.
“It was unclear what was a risk factor for what,” Vetter said.
To shed light on the question, researchers used data from female participants, average age 55, in the Nurses’ Health Study.
In 2009, all were free of depression. When asked about their sleep patterns, 37 percent described themselves as “early types,” 53 percent described themselves as “intermediate types,” and 10 percent described themselves as “evening types.”
The women were followed for four years to see who developed depression.
Depression risk factors like body weight, physical activity, chronic disease, sleep duration, or night shift work were also assessed.
The researchers found that late chronotypes, or night owls, are less likely to be married, more likely to live alone and be smokers, and more likely to have erratic sleep patterns.
After accounting for these factors, they found that early risers still had a 12 to 27 percent lower risk of being depressed than intermediate types. Late types had a 6 percent higher risk than intermediate types, although this finding was not statistically significant).
“This tells us that there might be an effect of chronotype on depression risk that is not driven by environmental and lifestyle factors,” said Vetter.
Research shows that our tendency to be an early bird, night owl, or somewhere in between is at least in part—12 to 42 percent—shaped by genetics. Some studies have already shown that specific genes (including PER2 and RORA), which influence when we prefer to rise and sleep, also influence depression risk.
“Alternatively, when and how much light you get also influences chronotype, and light exposure also influences depression risk,” Vetter said.
She stresses that while the study does suggest that chronotype is an independent risk factor for depression, it is “a small effect” and it does not mean night owls are doomed to be depressed.
Her advice to night owls who want to lower their risk?
Do your best to become an earlier bird.
Try to get enough sleep and exercise, spend time outdoors, dim the lights at night, and try to get as much light by day as possible.