Physically active men at work are more fertile, a Harvard study confirms

Men who regularly lift heavy objects at work have almost 50 percent higher sperm concentration and count.
Jijo Malayil
Man carrying a box
Man carrying a box


As infertility is becoming a common problem of late, and medical professionals are scrambling to find solutions to nullify this rising trend. Researchers have found a link between male fertility and occupational factors, such as physical demands and work schedules. 

The Harvard Medical School (HMS) and Brigham and Women’s Hospital collaborative effort found that men who "regularly lift heavy objects at work have higher sperm counts than men whose work is less physically demanding," a press release said. The study, published in the journal Human Reproduction, is "part of the Environment and Reproductive Health (EARTH) cohort, aimed to examine how environmental chemicals and lifestyle choices affect reproductive health."

The multiple benefits associated with exercise in humans is well known, including those observed on reproductive health, "but few studies have looked at how occupational factors can contribute to these benefits,” said first author Lidia Mínguez-Alarcón, HMS assistant professor of medicine at Brigham and Women’s and a co-investigator of the EARTH study.

40% of infertility cases are caused by factors affecting men

Data has shown that men are responsible for nearly half of the issues related to infertility. Factors such as sperm count, semen quality, and sexual function are found to be the main restricting factors for such a predicament. 

To substantiate it, a previous study done by the EARTH team found that among men seeking fertility treatment, sperm count and quality declined by as much as 42 percent between 2000 and 2017.

“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,” said Mínguez-Alarcón.

Physically active men at work have higher sperm concentration and count

The study was done using the data collected by the EARTH study, which was done by the Harvard T. Chan School of Public Health and Mass General Brigham, to gauge the impact of environmental and lifestyle factors on fertility. The study sourced medical information from over 1,500 men and women seeking medical assistance for infertility. The current study took a subset of 377 male partners in couples seeking treatment at a fertility center from the collected data. 

A thorough analysis revealed that men who reported more physically strenuous activities at work had 46 percent higher sperm concentration percent and 44 percent higher total sperm count compared to those with less physical jobs. Also, the according to the team, men who reported more physical activity at work had higher levels of the male sex hormone testosterone and, counterintuitively, 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. In this case, we hypothesize that excess testosterone is being converted into estrogen, a known way for the body to keep normal levels of both hormones," said Mínguez-Alarcón. The results proved that physically demanding jobs and rotating or evening shift occupations may be associated with higher testicular function in men measured as higher sperm concentrations and counts and higher serum testosterone and estradiol levels.

The team plans to confirm if these findings will hold for men from the general population. The researchers also hope future studies will reveal the underlying biological mechanisms. “Uncovering actionable steps people can take to improve their fertility stands to benefit all of us, not just couples trying to conceive," according to Mínguez-Alarcón.

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