Men who regularly lift heavy objects at work have higher sperm counts, according to a new study from researchers at Brigham and Women’s Hospital.
The Boston scientists found that occupational factors, such as physical demands and work schedules, were associated with higher sperm concentrations and serum testosterone in men in the Environment and Reproductive Health (EARTH) clinical trial.
“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 may contribute to these benefits,” said first author Lidia Mínguez-Alarcón, a reproductive epidemiologist. in 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 a significant improvement in male reproductive performance,” Mínguez-Alarcón added.
Infertility is a growing problem and can be caused by a wide variety of factors. However, about 40% of infertility cases can be traced to male factors such as sperm count, sperm quality and sexual function.
In particular, sperm count and sperm quality are considered to be the main causes of increasing infertility in men. A previous analysis led by the EARTH research team found that in men seeking fertility treatment, sperm count and quality dropped by as much as 42%. between 2000 and 2017.
“Furthermore, there is increasing evidence that male infertility is associated with common chronic diseases such as cardiovascular disease and autoimmune diseases, highlighting the broader importance of male reproductive health,” Mínguez-Alarcón said.
The EARTH study is a collaboration between the Harvard T. Chan School of Public Health and Mass General Brigham to evaluate the effect of environmental and lifestyle factors on fertility.
EARTH collected samples and survey data from more than 1,500 men and women, and the current study focused on a subset of these participants, including 377 male partners in couples seeking treatment at a fertility center.
The researchers found that men who reported frequently lifting or moving heavy objects at work had a 46% higher sperm concentration and 44% higher total sperm count compared to men with fewer physical jobs. Men who reported more physical activity at work also 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,” Mínguez-Alarcón said. “In this case, we hypothesize that excess testosterone is converted to estrogen, which is a known way for the body to maintain normal levels of both hormones.”
While the current study found an association between physical activity and fertility in men seeking fertility treatment, further research will be needed to confirm whether these findings hold for men in the general population. The researchers also hope that future studies will reveal the underlying biological mechanisms.