‘Damage due to air pollution’ leads to lower sperm counts

Previous studies have linked reproductive issues and a range of other conditions — including obesity and diabetes — to the harmful substances inhaled by humans.

Dave Yasvinski 3 minute read October 25, 2021
watercolour smoke stacks

Air pollution contributes to roughly 15,300 premature deaths every year. GETTY

A new study has found that air pollution’s toxic effect on fertility is caused by inflammation in the brain that lowers sperm counts and makes it more difficult to conceive.

While previous studies have linked reproductive issues and a range of other conditions — including obesity and diabetes — to the harmful substances inhaled by humans, the current research, conducted on mice and published in the journal Environmental Health Perspectives, uncovers the mechanism at work and offers hope for future intervention.

“Our findings showed that the damage due to air pollution — at least to the sperm count — could be remedied by removing a single inflammation marker in the brains of mice, suggesting that we may be able to develop therapies that could prevent or reverse the damaging effects of air pollution on fertility,” said Zhekang Ying, lead author of the study and an assistant professor of Medicine at the University of Maryland School of Medicine.

According to Health Canada, air pollution contributes to roughly 15,300 premature deaths in the country every year at a total annual economic cost in the neighbourhood of $120-billion — the equivalent of six per cent of Canada’s 2016 gross domestic product. Around 92 per cent of the global population lives in areas of the world where the level of fine particles in the air smaller than 2.5 micrometers in diameter exceeds the safety standards established by the World Health Organization. Such particles are typically produced by industrial facilities, car emissions and wildfires.

Researchers were on the hunt for the mechanism driving the decrease in sperm counts after noticing that some mice that were exposed to air pollution did not always exhibit an inflammation of the testes. Well aware that the brain has a direct link to the sex organs, the team was interested in whether pollutants in the air could also be causing inflammation in the brain.

To test their theory, researchers subjected healthy mice and a group bred to lack a marker of inflammation in the brain, known as Inhibitor Kappa B Kinase 2 (IKK2), to filtered air or air pollution before testing their sperm counts. Mice whose neurons were lacking IKK2 did not experience the same low sperm counts observed in healthy mice following exposure to pollutants. Further research pinpointed one specific type of neuron — typically associated with obesity and the sleep cycle — that was to blame for the pollution-induced decline in sperm.

These neurons are generally located in the hypothalamus, the part of the brain responsible for hunger, thirst and sex drive. The hypothalamus works closely with the pituitary gland, an area of the brain that produces hormones that act on the reproductive system.

“Looking back, it makes perfect sense that the neurons in the hypothalamus are the culprits perpetuating this inflammation response that results in low sperm count, as we know that the hypothalamus is a major pathway link between the brain and the reproductive system,” Ying said.

Now that they understand part of the mechanism behind the body’s response to elevated air pollution, researchers hope their work will open new avenues to addressing reproductive issues and, perhaps, a host of other conditions.

“These findings have wider implications than just fertility, as there are many conditions, such as high blood pressure, diabetes and heart disease that can result from brain inflammation due to air pollution,” said Charles Hong, professor in medicine and director of cardiology research at UMSOM.

Dave Yasvinski is a writer with Healthing.ca