Rapidly rising infertility rates have been a growing concern worldwide, and researchers have been prodding to find answers.
According to a National Institute of Health publication, up to 40 to 50 per cent of the cases can be traced to male factors, including low sperm count, poor semen quality, and dysfunctional sex organs.
But now researchers from the Harvard-affiliated Brigham and Women's Hospital have discovered that men who regularly lift heavy objects at work have nothing to do with the declining sperm counts.
Men who regularly do physically taxing jobs have more sperm. The study findings were published in the journal 'Human Reproduction' as part of the Environment and Reproductive Health (EARTH) cohort, a clinical study exploring how exposure to environmental toxins and lifestyle choices affect reproductive health.
"We already know that exercise has multiple health benefits to humans, including on their reproductive health, but few studies have explored how occupational factors contribute to these benefits," said the lead author Lidia Minguez-Alarcon, a reproductive epidemiologist in Brigham's Channing Division of Network Medicine and co-investigator of the EARTH study during her presentation of the findings.
"What these new findings infer is that physical activity during work is also associated with significant improvement in men's reproductive potential."
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EARTH surveyed samples and data from over 1,500 men and women.
The researchers discovered that men who reported often lifting or moving heavy objects at their workplace had 46 per cent higher sperm concentration and 44 per cent higher total sperm count compared to those with less physical activity work.
Men who reported more physical activity at their workplace also had higher levels of the male sex hormone testosterone and the female hormone estrogen.
"Contrary to what some people recall from biology class, 'male' and 'female' hormones are found in both sexes, but in different amounts," explained Minguez-Alarcon. "In this case, we hypothesize that the excess testosterone is converted into estrogen, which is a known way for the body to balance and maintain normal levels of both hormones."
A previous analysis led by the EARTH research team discovered that among men seeking fertility treatment, sperm count and quality declined by up to 42 per cent between 2000 and 2017.
They also discovered common chronic diseases such as cardiovascular disease and autoimmune disease contribute to male infertility.
"Reproductive health is critical in its own right, but growing evidence suggests that male infertility can provide deeper insight into broader public health issues, including common chronic conditions," said Minguez-Alarcon.
"Uncovering actionable measures people can take to improve their fertility stands to benefit everyone, and not just couples trying to conceive."