Previous studies have shown exercise can have a positive effect on reproductive health, but few have studied how occupational factors contribute.

Findings from the Environment and Reproductive Health (EARTH) Study suggest men with more physically demanding occupations, including regularly lifting heavy objects, have higher sperm counts than men with less physically demanding work.

The study, published in Human Reproduction and summarized in a Brigham and Women’s Hospital press release, was led by Lidia Mínguez-Alarcón, PhD, a reproductive epidemiologist in the Brigham’s Channing Division of Network Medicine, and Jorge Chavarro, MD, ScM, researcher at the Brigham and professor of Nutrition and Epidemiology at the Harvard T.H. Chan School of Public Health.

The EARTH Study evaluates the effects of environmental and lifestyle factors on fertility. Infertility is a growing problem, and about 40% of infertility cases have been traced to male factors. A previous analysis published in Environment International by the EARTH team found that among men seeking fertility treatment, sperm count and semen quality declined 42% between 2000 and 2017.

The current study focused on a subset of the 1,500 EARTH participants, including 377 male partners in couples seeking treatment at a fertility center.

The researchers found men who reported regularly lifting or moving heavy objects at work had a 46% higher sperm concentration and 44% higher total sperm count compared to men with less physically demanding occupations. Men who reported more physical work also had higher levels of testosterone and estrogen, which the researchers hypothesize results from the body converting excess testosterone into estrogen to maintain normal levels of both hormones.

Although this study indicates a relationship between physical activity and fertility in men seeking fertility treatment, future research is needed to confirm if the same applies to the general population. These findings highlight the broader importance of understanding male reproductive health and the actionable steps people can take to improve their fertility.