Blue-Collar Jobs Increase Fertility in Men: Study

Men work at a construction site in downtown Toronto, Canada, on June 30, 2016. The Canadian Press/Eduardo Lima

Men who do more physically demanding jobs involving heavy lifting are more likely to have higher sperm counts and testosterone levels, according to a new study published in the journal Human Reproduction.

Researchers from Brigham and Women’s Hospital in Boston collected samples and survey data from more than 1,500 men and women, focusing on a subset of these participants, including 377 male partners in couples seeking treatment at a fertility center between 2005 and 2019.

The men self-reported information regarding their lifting and moving of heavy objects, typical shifts, and physical level of exertion at work via a take-home questionnaire.

Semen samples were then analyzed and enzyme immunoassays, a widely used diagnostic tool, were used to assess reproductive hormone concentrations.

Researchers 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 compared to men who reported never lifting or moving heavy objects at work.

Similar results were also found for men who worked in rotating shifts compared to those in day shifts, as well as for men involved in heavy levels of physical exertion compared to those with light levels at work.

More Physical Activity, More Testosterone

In addition, males who reported more physical activity at work also had higher levels of the male sex hormone testosterone and, surprisingly, the female hormone estrogen.

The latest research is part of the Environment and Reproductive Health (EARTH) cohort, a clinical study exploring how exposure to environmental chemicals and lifestyle choices affect 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,” said first author Lidia Mínguez-Alarcón, a reproductive epidemiologist at Brigham’s Channing Division of Network Medicine and co-investigator of the EARTH study.

“What these new findings suggest is that physical activity during work may also be associated with significant improvement in men’s reproductive potential,” Mínguez-Alarcón said.

Mínguez-Alarcón also noted that male and female hormones can be found in both men and women, albeit in varying amounts, and the study authors believe that in the case of the man they analyzed, the excess testosterone is being converted into estrogen.

While the latest study appears to suggest a link between more physically demanding roles and increased sperm counts in men, the authors acknowledge that the findings may not be generalized to all of the male population, given that the study only recruited men from couples seeking fertility treatment.

In addition, the authors note that there may have been errors or misclassification in the self-reported questionnaires which could impact the outcome of the study.

“Confirmation of these findings in other non-fertility clinic study populations is warranted,” the researchers wrote.

Global Sperm Counts Plummet

The study was funded by grants from the National Institutes of Health (NIH) and from the National Institute of Environmental Health Sciences (NIEHS) and Legacy, Inc.

Men are considered to have a low sperm count if they have less than 15 million sperm per milliliter or less than 39 million sperm total per ejaculate, according to the Mayo Clinic.

According to the Cleveland Clinic, infertility affects one in every six couples who are trying to conceive.

A separate study published in November 2022, led by professor Hagai Levine of the Hebrew University of Jerusalem’s Hadassah Braun School of Public Health, found that sperm counts worldwide have halved over the past 45 years.

That study analyzed 223 other studies based on sperm samples taken from over 57,000 men across 53 countries, including the United States, Europe, and Australia, between 1973 and 2018.

It found an “appreciable decline” in sperm count during that time period, with total sperm counts falling by 62.3 percent during the same period.

Researchers in that study declared the “substantial and persistent decline” in sperm count a “significant public health concern” and called for more research to prevent “further disruption of male reproductive health.”

According to the Centers for Disease Control and Prevention (CDC), an array of factors can impact men’s fertility, including age, smoking, excessive alcohol and drug use, obesity, and exposure to environmental toxins such as pesticides, lead, cadmium, or mercury.