Exposure to common air pollutants may alter the function of sperm genes, according to one of the largest fertility studies of its kind. The research indicates that men exposed to pollutants during sperm development showed subtle DNA changes, potentially impacting male fertility and the health of their future children.
The study, presented at the European Society of Human Reproduction and Embryology's annual meeting in London, identified ozone and nitrogen dioxide as the pollutants most strongly associated with these genetic alterations. These findings point to DNA methylation as a key mechanism, a process where chemical tags attach to DNA and regulate gene activity without changing the underlying genetic code.
Scientists analyzed sperm DNA methylation in 1,220 men in Salt Lake City, Utah, who provided samples between 2013 and 2017. Researchers estimated participants' exposure to outdoor pollutants, including ozone, nitrogen dioxide, sulfur dioxide, and fine particulate matter, during the three-month period of sperm production prior to each sample collection. The study identified 39 DNA changes linked to air pollution mixtures, with ozone and nitrogen dioxide showing the most significant influence.
One of the genes affected, GNAS, has previously been linked to reduced semen quality and impaired fetal development. Alterations in the paternal copy of GNAS have been associated with severe intrauterine growth retardation (IUGR), a condition where a baby is born significantly smaller than expected for its gestational age. IUGR increases the risk of stillbirth, premature birth, brain injury, and other lifelong health complications.
"Because imprinted genes can persist through early embryonic development, this raises important questions about whether fathers' environmental exposures may influence not only fertility, but pregnancy and offspring health," said Dr. Carrie Nobles, an epidemiologist at the University of Massachusetts Amherst and lead author of the study.
Air pollution levels vary by location and season. According to the American Lung Association's 2026 State of the Air report, approximately 152 million Americans, nearly half the country, live in areas with unhealthy levels of ozone or particle pollution. Ozone levels tend to be higher on hot, sunny days, while pollutants like particulate matter can be more common in winter. Nitrogen dioxide, largely a byproduct of vehicle exhaust and fossil fuel combustion, is a constant concern in urban centers, where it is often generated by traffic and the use of natural gas for heating and power.
Megan E. Nobles stated that future research should focus on replicating these findings in other populations and investigating whether the observed DNA changes have measurable impacts on fertility and pregnancy outcomes. Karen Sermon, immediate past chair of the European Society of Human Reproduction and Embryology, noted that this research adds to the understanding of how pollution affects reproductive health, potentially explaining difficulties couples face in conceiving when exposed to polluted environments.