Ozone and nitrogen dioxide appear most strongly associated with epigenetic changes in sperm, affecting male reproductive health
Air pollution is linked to alterations to sperm DNA, according to research unveiled today at the European Society of Human Reproduction and Embryology conference in London.
The study, among the largest of its kind examining fertility, found that exposure to common atmospheric pollutants during sperm development produced subtle genetic modifications.
These changes affected whether certain genes were activated or deactivated, prompting renewed concerns about the potential impact of polluted air on male reproductive health.
Ozone and nitrogen dioxide emerged as the pollutants most strongly associated with these epigenetic alterations, according to findings presented on Tuesday at the annual gathering.
The investigation tracked more than 2,000 men residing in Salt Lake City, Utah, over a four-year period from 2013 to 2017.
Participants submitted semen samples upon joining the study, with further collections at two, four and six-month intervals.
Scientists calculated each man's exposure to various outdoor pollutants during the three months preceding each sample, a timeframe that corresponds with the sperm production cycle.
The pollutants assessed included ozone, nitrogen dioxide, sulphur dioxide and fine particulate matter.
Dr Carrie Nobles, an epidemiologist at the University of Massachusetts Amherst who led the research, said: "Our findings suggest that air pollution exposure during key stages of sperm development may be associated with changes in sperm DNA."
While mounting evidence has suggested atmospheric pollution may diminish male fertility, the underlying biological mechanisms have remained elusive.
This latest research points to DNA methylation as a potential explanation. These are chemical markers attached to DNA that control gene activity without altering the genetic code itself.
Analysis of sperm DNA methylation from 1,220 participants who provided samples at the six-month stage identified 39 distinct DNA modifications linked to pollution exposure.
Although most epigenetic markers are wiped clean during early embryonic development, certain genes retain these "imprinted" changes, potentially influencing foetal growth.
One gene identified, GNAS, has previously been connected to reduced semen quality and developmental outcomes.
Dr Nobles stressed the importance of continued investigation in this field, stating: "Changes in gene expression have the potential to impact men's fertility, which is why this area of research is important.
"Future work is needed to make a direct link between air pollution-associated changes in sperm DNA methylation and fertility."
Prof Allan Pacey, a professor of andrology at the University of Manchester who was not involved in the study, acknowledged the research demonstrated a measurable effect.
"At the present time, it is not possible to conclude whether the observed changes to sperm DNA methylation are clinically meaningful for male infertility, and further work will need to be done to confirm or refute that," he added.
Prof Richard Lea, a reproductive biology expert at the University of Nottingham, described it as significant research contributing to growing evidence that airborne pollutants adversely affect sperm quality.
