Study links physically demanding jobs to higher male fertility

Boston — Regularly lifting and moving heavy objects at work is associated with higher levels of male fertility, results of a recent study by researchers at Brigham and Women’s Hospital show.

The study involved 377 male participants who were part of a couple seeking treatment at a fertility center and enrolled in the Environment and Reproductive Health (EARTH) study between 2005 and 2019. 

The men with more physically demanding jobs had a 46% higher sperm concentration and a 44% higher total sperm count than those in less physical jobs. They also had higher levels of both testosterone and estrogen. The researchers speculate that excess testosterone is converted to estrogen as the body attempts to keep normal levels of both hormones.

Previous analysis of the EARTH study shows that men seeking fertility treatment saw a 42% decline in sperm count and quality between 2000 and 2017. About 40% of infertility cases are caused by male factors, including sperm count, semen quality and sexual function, the researchers said.

In a press release, study co-author Lidia Minguez-Alarcón, a reproductive epidemiologist in Brigham’s Channing Division of Network Medicine, notes that male infertility is increasingly being associated with common chronic diseases, including cardiovascular disease and autoimmune disease.

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

The study was published online in the journal Human Reproduction.