As air pollution found to cause DNA changes in sperm, what male fertility factors can you control

New research presented at the European Society of Human Reproduction and Embryology (ESHRE) conference has found a direct link between air pollution and changes to the DNA of sperm cells. For men trying to conceive, or thinking ahead about future fertility, it’s a reminder that reproductive health is shaped by environment as much as biology. It’s also a reminder that several of the factors involved are within our control.

What the study found

Researchers at a US university analysed semen samples from over 1,220 men in Salt Lake City, Utah, comparing DNA methylation patterns against local air pollution levels during the three months it takes sperm to develop. Methylation doesn’t alter the DNA sequence itself, but it can switch genes on or off. The study found that sperm developing during periods of higher pollution were more likely to carry these changes.

One affected gene, GNAS, is linked to sperm quality and is also imprinted, meaning it carries specific parental markers that can persist into early embryonic development. Ozone and nitrogen dioxide showed the strongest associations with methylation changes.

Lead author Dr Carrie Nobles was clear that more research is needed: it isn’t yet known whether these methylation changes have a measurable effect on fertility or pregnancy outcomes.

What the research does add is a plausible mechanism for something scientists have suspected for some time: that air pollution and male fertility are connected, and that a father’s environment in the months before conception may matter for more than his own health.

What you can control

Air quality isn’t something most men can change day to day, and the study is a useful reminder that fertility isn’t purely a matter of individual choices. Sperm take around three months to develop, so lifestyle during that window has a real, measurable effect on the sperm produced at the end of it. Five factors carry the strongest evidence.

Diet and male fertility:

Diets high in processed food, saturated fat and sugar are associated with poorer sperm concentration and motility. Diets rich in fruit, vegetables, whole grains and omega-3 fats are linked to better semen parameters. Antioxidants, found in foods like berries, leafy greens and nuts, help protect sperm from oxidative damage, and maintaining a healthy weight is one of the more consistent findings in the research on male fertility.

Sleep and your sperm:

Both too little and too much sleep have been linked to lower sperm count and quality, likely through their effect on testosterone production, which follows a daily rhythm and is disrupted by irregular or insufficient sleep. Seven to nine hours a night is a reasonable target.

Alcohol consumption and infertility:

Heavy or regular alcohol consumption is associated with reduced sperm count, poorer motility and increased abnormal sperm shape. The evidence is strongest at higher intake levels, so cutting back in the months before trying to conceive is a sensible precaution, even where the picture at moderate levels is less clear.

Smoking and sperm production:

This has some of the most consistent evidence among lifestyle factors. Smoking is linked to lower sperm count, reduced motility and higher levels of DNA fragmentation. Quitting is one of the more impactful changes a man can make to his fertility, and improvements can show up within the three-month sperm production cycle.

Heat’s impact on male fertility:

Sperm production works best a few degrees below core body temperature, which is why the testes sit outside the body. Regular hot baths, saunas, hot tubs, tight underwear and laptops used directly on the lap can all raise scrotal temperature. The evidence here is more mixed than for smoking or diet: some studies find measurable effects on semen parameters, others don’t.

The bigger picture

None of these factors guarantees an outcome on their own, and none should be read as reasons for self-blame if conception is taking longer than expected. Male fertility is complex, and this new research is a reminder that it’s shaped by exposures largely outside anyone’s control.

What the evidence does support is that diet, sleep, alcohol, smoking and heat are the areas where change is realistic and where the research is strongest, particularly in the three months before trying to conceive. Taken together, they’re a useful starting point rather than a checklist, and worth discussing with a specialist if you’re planning treatment or investigating unexplained delays in conceiving.

If you have questions about male fertility, sperm quality or want a clearer picture of where you stand, our male fertility assessments can help.