Researchers examined data from seven previously published studies of work schedules and mental health involving a total of 28,438 participants. Overall, shift workers were 28% more likely to experience mental health problems than people with consistent weekday work schedules.

“We know that shift-work alters the circadian rhythm, that is our normal sleep-wake cycle which matches day-night cycle,” said Luciana Torquati, lead author of the study and a researcher at the University of Exeter in the UK.

“This disruption can make people moody and irritable, and lead to social isolation as shift-workers time-off matches family and friend’s work and life commitments,” Torquati said by email.

In particular, the study found, shift workers were 33% more likely to have depression than people who didn’t work nights or irregular schedules.

Shift workers also had a higher chance of developing anxiety, but in this case the difference was too small to rule out the possibility that it was due to chance.

Women appeared particularly vulnerable to the negative mental health effects of shift work, researchers report in the American Journal of Public Health.

Compared to women who worked consistent weekday schedules, women who worked nights or split shifts were 78% more likely to experience adverse mental health outcomes.

Men, however, didn’t appear to have an increased risk of mental health issues when they worked nights or irregular schedules.

The study wasn’t a controlled experiment designed to prove whether or how work schedules might directly impact mental health.

It’s possible that people with poor mental health wound up in jobs with irregular schedules, rather than developing mood disorders after they started working nights or inconsistent shifts.

Even so, the results suggest that workers and employees should be aware of the potential for work schedules to impact mental health, Torquati said.

“Your brain is programmed to sleep during night hours (absence of light) to recover from all the information it has processed during the day,” Torquati said. “Conversely, day light tells your brain it’s time to be awake and process information.”

“With shift-work you turn this cycle upside down: process information & being awake at night, sleep during the day, and this means that body functions that follow such cycle are disrupted,” Torquati added. “This disruption of functions can result in irritability, nervousness, depressed mood, and ultimately mental disorders.”

It’s possible that shift work might be just one aspect of poor mental health, and people who suffer from symptoms of depression or other mood disorders should seek treatment, Torquati advised.

Finding time to exercise, get outside during daylight hours, and spend time with family and friends may also help improve mood and limit social isolation that can exacerbate depression, Torquati said.

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