Blue collar benefits: Jobs that require heavy lifting boost male fertility

BOSTON — Plenty of studies warn of the dangers associated with office jobs and sitting all day long. Now, researchers from Brigham and Women’s Hospital are espousing the reproductive benefits of more physically demanding jobs for men — especially those that require them to lift heavy objects. Scientists say their findings show that men who habitually lift heavy objects at work have higher sperm counts.

This study is part of the greater Environment and Reproductive Health (EARTH) cohort, a clinical project focused on exploring how exposure to environmental chemicals and lifestyle choices impact reproductive health.

“We already know that exercise is associated with multiple health benefits in humans, including those observed on reproductive health, but few studies have looked at how occupational factors can contribute to these benefits,” says first study author Lidia Mínguez-Alarcón, a reproductive epidemiologist in Brigham’s Channing Division of Network Medicine and co-investigator of the EARTH study, in a media release. “What these new findings suggest is that physical activity during work may also be associated with significant improvement in men’s reproductive potential.”

Infertility continues to be a growing issue across the entire world. While infertility can be the result of a wide array of factors, roughly 40 percent of infertility cases have to do with elements of male fertility — including sperm count, semen quality, and sexual function. More specifically, researchers believe sperm count and semen quality are the top two major drivers of growing infertility rates among men. A previous analysis led by the EARTH study team even found that sperm count and quality has declined by as much as 42 percent between 2000 and 2017 among men seeking fertility treatment.

“Further, there is increasing evidence that male infertility is associated with common chronic diseases such as cardiovascular disease and autoimmune disease, highlighting the broader importance of male reproductive health,” adds Mínguez-Alarcón.

Demanding work leads to higher hormone levels

The EARTH study is a collaboration between scientists at the Harvard T. Chan School of Public Health and Mass General Brigham, aimed at evaluating the effects of environment and lifestyle factors on fertility. EARTH has collected samples and survey data from more than 1,500 men and women. This current study used a subset of those participants, including 377 male partners in couples seeking treatment at a fertility center.

Ultimately, the research team found that men who reported often lifting or moving heavy objects at work had 46 percent higher sperm concentration and 44 percent higher total sperm count in comparison to other men with less physical jobs. It’s worth noting that men working more physically demanding jobs also had higher levels of the male sex hormone testosterone and the female hormone estrogen.

“Contrary to what some people remember from biology class, ‘male’ and ‘female’ hormones are found in both sexes, but in different amounts,” Mínguez-Alarcón explains. “In this case, we hypothesize that excess testosterone is being converted into estrogen, which is a known way for the body to keep normal levels of both hormones.”

Study authors stress that while this project did detect a relationship between physical activity and fertility in men seeking fertility treatment, additional research is necessary to confirm whether or not these findings would also hold true for men among the general population. Future studies, hopefully, will reveal the underlying biological mechanisms at play here as well.

“Reproductive health is important in its own right, but more and more evidence suggests that male infertility can give us insight into broader public health issues, including the most common chronic diseases,” Mínguez-Alarcón concludes. “Uncovering actionable steps people can take to improve their fertility stands to benefit all of us, not just couples trying to conceive.”

The study is published in the journal Human Reproduction.