Women who wake up earlier are less likely to develop depression, according to new research.

A study published in the Journal of Psychiatric Research examined data from 32,000 nurses and found that women who woke up early were 12 to 27 percent less likely to develop depression compared to their late-waking colleagues. The data was obtained from the biannual Nurses’ Health Study, and it classified the women, whose average age was 55, as ‘depressed’ when they self-reported the condition, had been diagnosed by a physician, or were treating it with medication.

 

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The researchers wanted to study how depression interacts with chronotype, which is when you tend to sleep and wake.

In casual conversation, people often describe chronotype by saying they’re either an ‘early bird’ or a ‘night owl,’ though many fall somewhere between the two. Some propose we should have more than two categories, like sleep expert Michael Breus, who popularized a more detailed breakdown of chronotype that divides it into four broad categories—dolphin, lion, bear, and wolf—each of which describe times of day when people tend to be most alert.

In any case, the new study shows that chronotype, which is influenced partly by genetics, may cause depression in women—even after controlling for other factors like smoking and living alone.

“This tells us that there might be an effect of chronotype on depression risk that is not driven by environmental and lifestyle factors,” lead author Céline Vetter, told The Independent. “Alternatively, when and how much light you get also influences chronotype, and light exposure also influences depression risk.”

Vetter, whose team comprises researchers from the University of Colorado at Boulder and Brigham and the Women’s Hospital in Boston, said night owls shouldn’t be alarmed by the findings.

“Yes, chronotype is relevant when it comes to depression but it is a small effect.”

The study is far from the first to examine how depression and sleep interact. It’s complicated, though, because it’s not always clear whether poor sleep habits causes depression or vice versa. Past studies have shown:

Vetter offered some advice to the night owls:

“Try to get enough sleep, exercise, spend time outdoors, dim the lights at night, and try to get as much light by day as possible.”

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