Air Pollution Linked to Sperm Gene Function Changes, Study Finds

Air pollution appears to alter how sperm genes function, one of the largest fertility studies of its kind has found.

Men exposed to common air pollutants while sperm were developing showed subtle DNA changes that affected whether genes were switched on or off, raising fresh concerns air pollution may harm male fertility.

The findings, presented on Tuesday at the annual meeting of the European Society of Human Reproduction and Embryology in London, identified ozone and nitrogen dioxide as the pollutants most strongly linked to these so-called epigenetic changes.

Dr Carrie Nobles, an epidemiologist at the University of Massachusetts Amherst, who led the work, said: “Our findings suggest that air pollution exposure during key stages of sperm development may be associated with changes in sperm DNA.”

The study followed more than 2,000 men in Salt Lake City, Utah, between 2013 and 2017. Participants provided semen samples when they enrolled and again after two, four and six months.

Researchers estimated each participant’s exposure to outdoor air pollutants – including ozone, nitrogen dioxide, sulphur dioxide and fine particulate matter – during the three months before each sample was collected, corresponding to the period of sperm production.

Growing evidence suggests air pollution could reduce male fertility but the biological mechanisms have been unclear. The latest work points to DNA methylation – chemical tags attached to DNA that regulate whether genes are switched on or off without changing the genetic code – as one possible explanation.

Scientists analysed sperm DNA methylation in the 1,220 men who provided a sample at the six-month follow-up. They identified 39 DNA changes linked to air pollution mixtures, with ozone and nitrogen dioxide appearing to have a strong influence.

Most epigenetic tags are erased early in embryo development but some genes are “imprinted” with these changes, meaning they have the potential to influence embryo development and beyond. One of the genes identified, GNAS, has previously been linked to poorer semen quality and foetal development.

Nobles said: “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 work, said the study had shown 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 professor of reproductive biology at the University of Nottingham, said: “This is an important piece of research that adds to a growing body of evidence that sperm quality is adversely affected by airborne pollutants.”