A new study from researchers at Brigham and Women’s Hospital, a founding member of Brigham’s Mass General health care system, suggests that men who regularly lift heavy objects at work have higher sperm counts. The study, published in Human Reproductionas part of the Environment and Reproductive Health (EARTH) cohort, a clinical study that aims to explore how exposure to environmental chemicals and lifestyle choices affect reproductive health.
“We already know that exercise is associated with numerous health benefits in humans, including those observed for reproductive health, but few studies have looked at how occupational factors can contribute to the benefits this,” said first author Lidia Mínguez-Alarcón, a reproductive epidemiologist in the Channing Division of Brigham Network Medicine and co-investigator of the EARTH study. “What these new findings suggest is that physical activity during labor may be associated with a significant improvement in male reproductive capacity.”
Infertility is a growing problem, and can be the result of a wide variety of complex factors. However, about 40% of infertility cases can be traced to male factors, such as sperm count, semen quality and sexual function. In particular, sperm count and semen quality are thought to be the main reasons for increasing infertility rates among men — a previous analysis by the EARTH study team found a decrease of as much as 42% among men seeking fertility treatment , sperm count and quality. % between 2000 and 2017.
“In addition, there is increasing evidence that male infertility is associated with common chronic diseases such as cardiovascular disease and autoimmune disease, emphasizing the wider importance of male reproductive health,” said Mínguez-Alarcón.
The EARTH study is a collaboration between the Harvard T. Chan School of Public Health and Brigham General Mass. to evaluate the effect of environmental and lifestyle factors on fertility. EARTH has collected samples and survey data from more than 1,500 men and women, and the current study focused on a subset of those 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 a 44% higher total sperm count compared to those who had less physical jobs. Men who reported more physical activity at work had higher levels of the male sex hormone testosterone and, counterintuitively, the female hormone estrogen.
“As some people remember from biology class, ‘male’ and ‘female’ hormones are found in both sexes, but in different amounts,” said Mínguez-Alarcón. “In this case, we hypothesize that too much testosterone is being converted into estrogen, which the body knows to maintain normal levels of both hormones.”
Although the current study found a relationship between physical activity and fertility in men seeking fertility treatment, further research will be needed to confirm whether these findings hold true for men from the general population. The researchers also hope that future studies will reveal the underlying biological mechanisms at play.
“Reproductive health is important in its own right, but more and more evidence suggests that male infertility can give us insight into broader public health issues, including the most common chronic diseases,” said Mínguez- Alarcon. “It will benefit us all, not just couples trying to conceive.”