Overnight shift work and heavy lifting impact women’s fertility, study says

Working overnight shift work was also found to increase the risk of ovarian and breast cancer, studies say.
Working overnight shift work was also found to increase the risk of ovarian and breast cancer, studies say. Getty Images

Women who work night shifts or jobs that are physically demanding may be hurting their chances of getting pregnant, a new study by Harvard University’s T.H. Chan School of Public Health says.

According to researchers, non-daytime work shifts may decrease women’s fertility, more so in overweight and obese woman and older women over 37 years.

“We’re not entirely sure of the biological mechanisms that are underlying this but it seems that physically demanding work on top of an obesogenic or overweight environment are two combined stressors that seem to be really detrimental to a woman’s ability to get pregnant,” said co-author Audrey Gaskins, research associate at the School of Public Health.

READ MORE: Census 2016: Fertility takes a back seat to immigration in Canada’s growth

The study looked at 500 women who were going through infertility treatments at the Massachusetts General Hospital between 2004 and 2015. This, they say, allowed them to directly measure several biomarkers of fecundity – the biological capacity for reproduction – that cannot be measured in women attempting to conceive naturally.

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The biomarkers researchers focused on were the number of antral follicles (small structures in the ovary that tell the number of immature eggs that remain in the ovary), the levels of follicle-stimulating hormone FSH, estrogen levels and the number of mature eggs capable of developing into healthy embryos.

Researchers then analyzed the association between the biomarkers and the physical demands and schedules of the jobs the women had, which they outlined in a questionnaire.

What the study found was that women who moved or lifted heavy loads at work had 8.8 per cent fewer total eggs and about 14 per cent fewer mature eggs than women who reported not doing such labour at work.

This was also the case for women who worked non-daytime schedules and rotating shifts.

However, researchers did not find any correlation between occupational factors, estrogen or FSH levels.

Researchers do not know why heavy lifting could affect a woman’s egg quality. However, in terms of why night shift work could be impacting egg yields, they speculate that it may have something to do with a disrupted internal body clock.

“We really need to do more research to see if these effects are short term or a longer lasting effect,” Gaskins says. “When we observe that such common occupational factors such as non-daytime shift work and moving or lifting heavy objects are detrimental, it’s a little alarming because so many women are potentially exposed to this.”

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Gaskins hopes the results of this study get both women and workplaces thinking and talking about women’s health.

“It’s very relevant from a policy and guidelines perspective so at this point I’d say it’s worth [for women] to talk to their supervisor if you’re concerned about these exposures,” Gaskins says.

This study echoes a previous 2013 report by the European Society of Human Reproduction and Embryology which found that shift work patterns may increase the risk of subfertility and disruption of women’s menstrual cycles.

READ MORE: Fertility, pregnancy and chronic illness: what you need to know

After looking at the data of over 199,000 women, researchers concluded women have a 33 per cent higher rate of menstrual disruption than those who work regular hours, as well as an 80 per cent increased rate of subfertility.

And while women who worked only nights did not yield the same results, they did have an increased rate of miscarriage.

Besides fertility, overnight and shift work has also been linked to other women’s health issues.

In a 2011 study, researchers at the Heart and Stroke Foundation of Canada found that women shift workers were at a higher risk of heart disease. In fact, they found that one in five middle-aged women who did shift work have at least three indicators of heart disease (like high blood pressure, obesity and metabolic syndrome).

That same year, a study in PLOS Medicine concluded that rotating night-shift work is associated with an increase risk of type two diabetes in women.

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Women are also at an increased risk of ovarian cancer and are twice as likely to get breast cancer, two separate studies by BMJ reported in 2013.