Shift work can harm men’s health more than women’s

Working nights can be hard on the body, and a new study suggests it could take a particular toll on men’s health.

The research, which involved laboratory mice and humans, indicates that the male of the species may be more vulnerable to the “body clock” disruptions associated with shift work.

In the lab, researchers found that male mice showed a range of negative effects from exposure to abnormal day-night cycles. Everything from their gene activity to their gut bacteria to their blood pressure spiraled out of control.

Female mice, on the other hand, seemed largely protected.

Then, using data from more than 90,000 shift workers in the UK, the researchers found that masculine men also seemed more affected. Men who worked nights were more likely than men who worked standard hours to get metabolic syndrome — a collection of risk factors for heart disease and diabetes, including elevated blood pressure, cholesterol and blood sugar, as well as excess fat around the middle.

Meanwhile, female shift workers were also at greater risk for metabolic syndrome than women who only worked standard hours. But that risk diminished after the researchers took into account the type of job, such as whether people worked shifts as medical professionals or factory workers.

The type of job matters because not all shift work is created equal, said study researcher Dr. Garret FitzGerald, a professor at the University of Pennsylvania Perelman School of Medicine, in Philadelphia.

There are different exposures depending on the job, he said, and differences in worker education and income, among others.

Together, FitzGerald said, the findings suggest that shift work may have less impact on the female body clock, though the reasons are not yet clear.

The laboratory experiments did point to a role for estrogen: female mice whose ovaries had been removed – and which therefore did not produce estrogen – were less protected against the impact of disrupted day-night cycles than female mice with normal estrogen production.

But that wasn’t the whole story, FitzGerald said, as male mice were still worse off.

The study, published May 17 in scientific translational medicine, is the latest to examine the potential drawbacks of shift work.

Past research has linked shift work to increased risks of high blood pressure, diabetes, heart disease and other ailments. It is thought that there may be indirect reasons – it is more difficult to eat healthily and exercise if you work at night – as well as direct effects of the day-night switch.

The human body’s natural circadian rhythms dictate that people be active and eat during the day, and sleep after dark. Shift work throws away those rhythms.

But some studies have also hinted that female shift workers may be more resistant to those effects than their male counterparts — with the latter showing more metabolic syndrome and diabetes.

The new study, FitzGerald said, took a closer look at the possible mechanisms. The lab portion showed that when male mice lost their circadian rhythms, the effects were wide-ranging. (The animals were also fed a high-fat diet, similar to the diet of many people who work night shifts.)

“What was striking was how ubiquitous the disturbance is,” FitzGerald said. “Genes, proteins, the bugs in the gut, blood pressure — all upside down.”

But female mice exposed to the same circadian disruption and a high-fat diet were largely unaffected.

The human portion of the study used data from the UK Biobank, a research project that collects genetic and health information on half a million middle-aged and older British adults.

The researchers identified more than 90,000 participants with a history of shift work and compared them to participants who had worked only standard hours. In men, about a third of shift workers had metabolic syndrome, compared to just over a quarter of non-shift workers.

The condition was generally less common in women and the difference between shift workers and other workers was smaller. Then, after the researchers took into account job type, there was no longer a significant difference between female shift workers and non-shift workers, FitzGerald said. But the difference between men remained.

While the human findings seem to support the lab findings, a sleep medicine specialist not involved in the study cautioned that it’s a big step from lab mice to people working shifts.

“I wouldn’t want people to interpret this as saying shift work isn’t bad for women,” says Dr. Sabra Abbott, an associate professor at Northwestern University Feinberg School of Medicine in Chicago.

“This suggests that shift work may be slightly less harmful to women, but we need more research to find out why,” Abbott said.

“It’s interesting that they saw this signal,” she added. “But it should be taken with a huge grain of salt.”

FitzGerald also stressed that the whole issue is complicated. Definitively linking disease risk to shift work is tricky, he said, because there are so many variables — including all the differences in education, income and daily exposure between people who have different types of work.

Both experts also said the findings highlight the potential health implications of shift work.

More generally, FitzGerald noted, everyone should be aware of the importance of “good sleep hygiene.” That includes getting sunlight during the day, he said, and turning off the devices — and their artificial lights — at night.

Health Day 2023. All rights reserved.