How air pollution may affect fertility

(CN) — Air pollution may affect sperm in ways scientists are still trying to understand.

Researchers say new findings published Monday in the Human Reproduction journal suggest it could also alter the way genes function in developing sperm, raising new questions about fertility and the health of future children.

Researchers found that men exposed to common outdoor pollutants during sperm development showed changes in DNA methylation, a chemical process that helps regulate how genes function without altering the DNA itself.

The study included more than 2,000 men in Salt Lake City, Utah, between 2013 and 2017. Participants provided semen samples at enrollment and again after two, four and six months, with researchers analyzing DNA methylation in sperm from the 1,220 men who completed the six-month follow-up.

The team estimated each participant’s exposure to outdoor air pollution during spermatogenesis, the approximately three-month process of sperm production.

They examined exposure to ozone, nitrogen dioxide, sulfur dioxide and fine particulate matter, pollutants commonly found in outdoor air.

Researchers identified 39 DNA methylation changes associated with mixtures of air pollutants. Ozone and nitrogen dioxide appeared to have the strongest associations.

Among the most notable findings were changes involving GNAS, an imprinted gene that has previously been linked to poorer semen quality and plays a role in embryonic and fetal development.

“Our findings suggest that air pollution exposure during key stages of sperm development may be associated with changes in sperm DNA methylation, including in genes involved in spermatogenesis and early developmental processes,” said lead author Carrie Nobles in a news release.

Previous research has linked air pollution to poorer semen quality, but researchers say far less is known about how pollution may influence sperm at the molecular level.

“The association with changes in the imprinted gene GNAS was particularly important,” Nobles said. “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.”

Researchers caution that the study found associations rather than proving that air pollution directly caused the genetic changes.

They also note air pollution is a complex mixture that varies by season and location. Nitrogen dioxide and ozone are often elevated in urban areas because of traffic emissions and natural gas combustion.

The findings add to growing evidence linking air pollution to reproductive health, according to Karen Sermon, professor and immediate past chair of the European Society of Human Reproduction and Embryology.

“This is another piece of the puzzle to understand how pollution negatively influences our fertility,” Sermon said in the news release. “We know that couples exposed to air pollution often have difficulties becoming pregnant, and this may be one of the explanations amongst the myriad ways that pollution impacts our reproductive health.”

Researchers say additional studies will be needed to determine whether the observed DNA methylation changes ultimately affect fertility or pregnancy outcomes.

“A critical next step is replication of findings in other studies,” Nobles said. “We also need to understand whether air pollution-associated changes in sperm DNA methylation have measurable downstream impacts on men’s fertility and couples’ pregnancy health. Future research should also explore the role of indoor and personal air pollution exposure.”