Air pollution has long been linked to a host of health issues, from respiratory problems to increased risk of cardiovascular disease. Now, researchers have uncovered fresh concerns: exposure to common outdoor air pollutants may also harm male fertility.
The study, presented at the European Society of Human Reproduction and Embryology in London, found that men exposed to high levels of ozone and nitrogen dioxide during sperm development experienced subtle DNA changes – known as epigenetic modifications. These changes can influence how genes are activated or deactivated without altering the underlying genetic code.
Researchers led by Dr Carrie Nobles at the University of Massachusetts Amherst tracked over 2,000 men in Salt Lake City between 2013 and 2017. Participants provided semen samples at regular intervals, with researchers estimating each individual's exposure to outdoor pollutants during key stages of sperm production. The study focused on ozone, nitrogen dioxide, sulphur dioxide, and fine particulate matter.
While previous research has suggested a link between air pollution and reduced male fertility, the mechanisms behind this association have been unclear. This latest study points to DNA methylation – a process involving chemical tags attached to DNA that regulate gene expression – as a possible explanation. In 1,220 men who provided a six-month follow-up sample, scientists identified 39 DNA changes linked to air pollution mixtures, with ozone and nitrogen dioxide showing a strong influence.
It's essential to note that these epigenetic tags are typically erased early in embryo development, but some genes can be 'imprinted' with these changes. One of the affected genes, GNAS, has previously been associated with poorer semen quality and foetal development. While this study suggests a measurable effect, Professor Allan Pacey cautions that it's unclear whether these observed changes are clinically significant for male infertility.
Professor Richard Lea highlights the significance of this research in adding to the growing evidence that airborne pollutants negatively affect sperm quality. Further investigation will be crucial to establish the full implications of air pollution on male fertility.