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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)

— "(We want) to look at whether a woman is able to change her schedule or lifting and whether we see a change in fecundity," Gaskins said, adding that this would determine whether the effect is short- or long-term. If stopping these exposures leads to an improvement, the team can make recommendations for policies.

"It's perhaps not surprising that people under more physical stress might have poorer fertility, but the big question is, why?" Channa Jayasena, a reproductive endocrinologist at Imperial College London who was not involved in the study, told CNN.

He cited previous studies showing that women who are malnourished or do extreme amounts of exercise, putting strain on their bodies, see adverse fertility effects. "It's possible this is an extension of that," he said.

But Jayasena added that although this study was interesting and insightful, greater sample sizes than the less than 500 in this study are needed to truly account for differences such as socioeconomic status.

"I think this tells us a limited amount," he said. "You need a study in the thousands."

Gaskins highlighted that the women were probably all of fairly high socioeconomic status, given that they were able to afford fertility treatment.

Another factor not accounted for was testosterone.

"In the study, no effort was made to address confounding by testosterone levels in those women. A physically stronger woman is more likely to undertake heavy lifting but would also be implicitly less fertile," said Alastair Sutcliffe, professor of pediatrics at University College London in the UK. "The typical and consistent differential between the sexes of strength is 10% to 15%, and this (is) accounted for by testosterone. Women also produce testosterone, albeit at a lower level than men."

One possible theory for the differences of shift work is disruption to a woman's circadian rhythm. Here, the researchers and Jayasena agree.

"It's certainly a very plausible mechanism," he said. "Each part of the body has its own circadian rhythm, including the ovaries."

Shift work has been proven to have a range of negative consequences on health, including increased risk of heart disease and obesity.

"Shift work is not a biologically good way to work," said Sutcliffe. "So what does this study mean? If trying to optimize fertility, stick to the day job and leave the lifting to their partner."