Pollution in the air we breathe may be lowering the fertility of men around the world, researchers have found.
Long-term exposure to PM2.5 air pollution—fine particulate matter in the air that is 2.5 micrometers or smaller in diameter—is linked to a greater risk of infertility in men, according to a new paper in The BMJ.
Road traffic noise pollution was also found to be linked to infertility in women over the age of 35, the paper said.
Infertility is defined as a lack of conception of a fetus after a year of unprotected and regular sex. It affects one in seven couples trying to conceive worldwide.
"Many of the established risk factors for infertility are similar for men and women and include advanced age (especially for women, where fertility drops rapidly after the late 30s), tobacco and alcohol use, sexually transmitted infections, various chronic conditions and diseases, obesity, and severe underweight. In addition, exposure to environmental factors, such as air pollution, pesticides, and ionizing radiation, are suspected risk factors for infertility," the researchers wrote in the paper.
The researchers analyzed data from 526,056 men and 377,850 women in Denmark who were likely to be trying to conceive (aged between 30 and 45, living with a partner, and with fewer than two children). They calculated the yearly average PM2.5 concentration and road traffic noise level at the address of every participant between 1995 and 2017, and they compared this data to the success of conception.
They discovered that exposure to PM2.5 at levels of 2.9 µg/m3 or higher across a five-year period was associated with a 24 percent increased infertility risk in men.
PM2.5 pollution particles are about 30 times smaller than the width of a human hair and can be made up of a variety of chemical components, such as dust, dirt, soot, smoke and liquid droplets. Sources of PM2.5 pollution include vehicle emissions, wildfires, coal burning, industrial processes and construction. Long-term exposure to high levels of PM2.5 has been found to increase the risk of chronic diseases, such as asthma, heart disease and lung cancer.
Previous studies have found links between pollution and sperm quality, but until now, links with the likelihood of conceiving have been inconsistent.
"In support of our results on PM2.5 and infertility in men, particulate air pollution (PM2.5 and PM10) has in recent studies been found to be negatively associated with factors defining sperm quality, including sperm motility and count as well as changes in sperm morphology. Our study therefore adds to these findings, showing that the effects of air pollution on sperm quality will potentially result in a higher risk of requiring assistance from a fertility clinic to achieve pregnancy," the researchers wrote.
The study also found that exposure to levels of road traffic noise of 10.2 decibels or higher on average over five years was associated with a 14 percent increased risk of infertility among women older than 35. Noise pollution was also found to slightly affect the fertility of men ages 37 to 45.
"Health effects of noise are suggested to be mediated through the triggering of a stress response, with activation of the autonomic nervous system and the hypothalamic-pituitary-adrenal axis, as well as through sleep disturbance. Both stress and sleep disturbance have been suggested to be associated with impaired reproductive function, including reduced sperm count and quality, menstrual irregularity, and impaired oocyte competence," the researchers wrote.
Both the effects of noise and pollution were found to be "consistent across people living in rural, suburban, and urban areas as well as across people with low, medium, and high socioeconomic status."
The study is only observational, meaning it cannot confirm causation. Still, it expands our knowledge of how modern life may affect fertility.
"This is an observational study and these are subject to some scientific constraints by their very nature. However, this was a large well-constructed study taking into account confounders," Jill Belch, an expert and professor in vascular medicine and air pollution at the University of Dundee's School of Medicine, said in a statement. "If validated by future prospective work then this association has striking implications for fertility as a 24 percent fall in male fertility and a 14 percent in female fertility would have very profound effects on future generations."
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References
Sørensen, M., Poulsen, A. H., Nøhr, B., Khan, J., Ketzel, M., Brandt, J., Raaschou-Nielsen, O. & Jensen, A. (2024). Long term exposure to road traffic noise and air pollution and risk of infertility in men and women: Nationwide Danish cohort study. BMJ, 386. https://doi.org/10.1136/bmj-2024-080664
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