Middle-aged and older women who are naturally early to bed and early to rise may be less likely to develop depression, according to a new study published in the Journal of Psychiatric Research.

Researchers at the University of Colorado (CU) Boulder and the Channing Division of Network Medicine at Brigham and Women’s Hospital in Boston evaluated the data of more than 32,000 female nurses. The study is the largest and most detailed observational study yet to investigate the association between chronotype (sleep-wake preference) and mood disorders.

The findings reveal that even after taking into account environmental factors such as light exposure and work schedules, a person’s chronotype — which is partly determined by genetics — appears to mildly influence depression risk.

“Our results show a modest link between chronotype and depression risk. This could be related to the overlap in genetic pathways associated with chronotype and mood,” said lead author Dr. Céline Vetter, director of the Circadian and Sleep Epidemiology Laboratory (CASEL) at CU Boulder.

Prior research has shown that people who stay up late are up to twice as likely to suffer from depression. But since those studies typically used data taken at a single point in time and didn’t account for many other factors that influence depression risk, it is still unclear whether depression leads people to stay up later or a late chronotype boosts risk of depression.

To find some answers, the researchers in this study looked at data from 32,470 female participants, average age 55, in the Nurses’ Health Study, which asks nurses to complete health questionnaires every other year.

In 2009, all the participants included in the study did not have 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 if anyone developed depression.

Depression risk factors such as body weight, physical activity, chronic disease, sleep duration, or night shift work were also taken into account.

The findings show 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, the researchers 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 (this modest increase 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.

Genetics are partly responsible for whether you are an early bird, intermediate type, or night owl, with research showing 12 to 42 percent heritability. And some research has found that certain genes (including PER2 and RORA), which influence when we prefer to rise and sleep, also affect depression risk.

“Alternatively, when and how much light you get also influences chronotype, and light exposure also influences depression risk. Disentangling the contribution of light patterns and genetics on the link between chronotype and depression risk is an important next step,” Vetter said.

But while the study does suggest that chronotype can factor into depression risk, it does not mean that night owls are doomed to be depressed.

“Yes, chronotype is relevant when it comes to depression but it is a small effect,” she said, noting that her study found a more modest effect than previous studies have.

Her advice to night owls who want to lower their risk?

“Being an early type seems to beneficial, and you can influence how early you are,” she said. 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.

Source: University of Colorado at Boulder