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Men Lifting Heavy Objects at Work Have Higher Sperm Count

A new study suggests having a higher sperm count may depend on your occupation.

Key takeaways:

Findings from Harvard T.H. Chan School of Public Health and Mass General Brigham show men with grueling occupations are more likely to have a higher sperm count than their peers.

So far, many similar studies have revolved around dietary details, and other factors including body mass index (BMI), waist circumference, and recreational physical activity.

Based on previous research, male factors account for 40% of infertility cases. According to the WHO, 48 million couples and 186 million individuals live with infertility.

Factors contributing to infertility in men can vary. The CDC lists older age, being overweight or obese, smoking, and alcohol consumption as lifestyle components lead to infertility.

Other elements leading to infertility include increased testosterone from medically prescribed injections or gels, radiation, and high-heat exposure. Also, medications such as flutamide, cyproterone, bicalutamide, spironolactone, ketoconazole, or cimetidine can lead to infertility. Exposure to environmental toxins, pesticides, lead, cadmium, or mercury can also increase the chances of infertility.

In the research published in Human Reproduction on February 11, investigators cite the lack of evidence on occupational factors affecting infertility. A review from the same publication published this past fall analyzed trends in men’s sperm count. They found the human sperm count has dropped by 51.6% in the last 50 years.

With low sperm counts contributing to infertility, researchers at Harvard-affiliated Brigham and Women’s Hospital were eager to find the impacts of one’s job on sperm count.

Male participants for the Harvard study were enrolled in the Environment and Reproductive Health (EARTH) cohort study. EARTH is currently analyzing environmental and dietary factors of fertility in couples seeking infertility treatment from the Massachusetts General Hospital (MGH) Fertility Center.

What the study found

Men between 18 and 56 in the EARTH database without a vasectomy were eligible for the Harvard research. Of those able to participate, 377 were included in the new study, with 145 men providing blood samples to measure certain reproductive hormones in serum. Participants had their weight, height, BMI, and additional lifestyle questions gathered at the beginning of the study.

Participants described their work schedule and physical demands on take-home surveys. Respondents answered questions about heavy-lifting involvement in their occupation with the options: never, sometimes, or often. Additionally, participants detailed their levels of physical exertion in their job with the options: light, moderate, and heavy.

In their findings, men who lift heavy objects often or at work contained a 46% greater sperm concentration. Active men held a 44% higher total sperm count compared to men with more sedentary jobs.

Men who were more active showed higher levels of the male sex hormone testosterone and the female sex hormone known as estrogen. First author and reproductive epidemiologist in Brigham’s Channing Division of Network Medicine, Lidia Minguez-Alarcon, Ph.D., M.P.H., says this is nothing unusual in a university release.

"Contrary to what some people remember from biology class, 'male' and 'female' hormones are found in both sexes, but in different amounts," Minguez-Alarcon said. "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."

Minguez-Alarcon believes the male infertility conversation is important, because it has been linked to chronic diseases featuring cardiovascular disease and autoimmune disease. She says it is important to find steps to reduce infertility.

In their discussion, Minguez-Alarcon and her team highlight past studies that found physically draining workplace activities contributed to lower sperm counts. However, the EARTH study used for the Harvard findings included individuals with lower sperm counts than in past investigations.

Harvard researchers do admit the study contains some slight limitations. Participants in the study were currently seeking fertility treatment, meaning the numbers might not be the same in a general population study. Also, only employed men received the opportunity to be involved in the study — not allowing researchers to compare sperm counts in employed versus unemployed men.

While the findings may provide some noteworthy information for men worried their physical activity may lead to higher sperm counts, researchers believe much is left to be discovered in the discussion.

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