Heavy lifting, shift work could harm women's fertility, study shows

2/15/2017, 6 a.m.
Jobs that involve heavy lifting on a regular basis could reduce a woman's fertility, particularly among overweight and obese women, ...
Nearly 60 percent of Black women worked in either the service industry, sales or office jobs. (Stock photo)

— Jobs that involve heavy lifting on a regular basis could reduce a woman's fertility, particularly among overweight and obese women, a new study shows.

The research, published Monday in the journal Occupational and Environmental Medicine, also found that working antisocial hours (in the evenings or night) or rotating shifts, may also impact female fertility.

Though the underlying cause is not known and more research is needed to further verify the findings, the team at the Harvard T.H. Chan School of Public Health believes that women in their reproductive years may need to consider this when trying to conceive.

"Our study suggests that women who are planning pregnancy should be cognizant of the potential negative impacts that non-day shift and heavy lifting could have on their reproductive health," said Lidia Mínguez-Alarcón, a research fellow in the Department of Environmental Health and lead author of the study, in a statement.

Recent studies have shown potential associations between physically demanding jobs or shift work and reduced fertility, but this new study explored direct biomarkers for fertility in the body, such as egg numbers and hormone levels, to suggest possible mechanisms behind the change.

Reduced egg count

The team of researchers studied more than 470 women having fertility treatment and compared the physical demands and schedules of their jobs against four biomarkers -- genes or characteristics in the body -- known to be linked to their ability to reproduce, also called fecundity.

The biomarkers were numbers of antral follicles, indicative of the number of immature eggs remaining in the body; levels of follicle-stimulating hormone that regulated reproductive processes; estrogen levels; and numbers of mature eggs capable of developing into healthy embryos.

The heavier the lifting or moving of objects the women reported doing in their jobs, the lower the number of antral follicles and mature egg: Women reporting heavy lifting and moving had 8.8% fewer total eggs and 14.1% fewer mature eggs compared with women who never lifted or moved heavy objects at work.

"These occupational exposures are affecting egg production and quality," said Audrey Gaskins, an epidemiologist at the Harvard T.H. Chan School and senior author on the paper told CNN.

This reduction in mature eggs was even greater in women who were also overweight, obese or over the age of 37.

"We saw this same association in an entirely different cohort," Gaskins said of a recent study by her team that also saw a link between obesity and reduced fertility. "We speculate it could be due to a disrupted stress-response system. Obesity affects the body's ability to handle stress."

People who worked nights or rotating shifts in the new study also saw a reduction in the number of mature eggs.

No association, however, was seen between these aspects of the women's occupation and their levels of follicle-stimulating hormone or estrogen.

Theories on differences

The mechanisms explaining this link to reduced fertility are not known, but the researchers would like to explore further, as well as looking at whether this impact on fertility could be improved, reduced or avoided.