Study: Smaller air pollution particles have a greater impact on men's semen quality

New research, based on an analysis of sperm from more than 30,000 men in China, suggests that air pollution may affect semen quality, specifically sperm motility (the ability of sperm to swim in the right direction). The study, published today in the Journal of the American Medical Association Online, shows that the smaller the size of air pollution particles, the greater the link to poor semen quality.

"Our results suggest that smaller particle size fractions may be more potent than larger particles in inducing low sperm motility," the authors wrote. "The researchers believe these findings highlight another reason to reduce air pollution exposure in men of reproductive age."

Researchers have long tried to determine if there is a link between air pollution and sperm quality, but it has been unclear whether the former has adverse health effects on male fertility because the findings are often inconsistent and complex to grasp. There does seem to be reason to believe that pollution may have a negative impact on fertility across the population, as suggested in this international literature review published in December 2021.

Researchers from Tongji University School of Medicine in Shanghai looked at data records of a total of 33,876 men from 340 cities in China, with an average age of 34, who were exposed to varying levels of air pollution and whose wives became pregnant using assisted reproductive technology using their sperm between January 2013 and December 2019.

They then looked for patterns in semen quality related to whether the participants had been exposed to particles less than 2.5 microns, 2.5 to 10 microns, and 10 microns in diameter at various key times in the 90 days before they came to the hospital for ejaculation. To determine semen quality, the researchers focused on factors such as sperm count, concentration, and sperm motility.

Although the researchers were unable to find a significant link between air pollution and sperm quality in terms of sperm count or concentration – they did find that the more exposure participants had to smaller particles, the lower both progressive and total sperm motility. Progressive sperm motility refers to the ability of sperm to swim forward, while total sperm motility simply refers to the overall swimming ability of the sperm.

Specifically, sperm motility was estimated to decrease by 3.6% when exposed to particles with a diameter less than 2.5 microns, while sperm motility decreased by 2.44% when exposed to particles with a diameter of 10 microns, suggesting that particle fractions of different sizes may have different effects on semen quality, perhaps because the smaller the particles, the more likely they are to penetrate deep into a person's lungs.

The data suggest that the effects of pollution were more prominent when exposure occurred during the initial 90-day period of sperm production – known as spermatogenesis – rather than during the other two phases. This in turn could mean that particulate matter affects sperm at a genetic level, the researchers say, but these are just speculations and more research needs to be done in this area.

Allan Pacey, professor of andrology at the University of Sheffield, who was not involved in the research, said: "Over the years, many studies have suggested the possibility of a link between air pollution and semen quality, although not all studies agree on this conclusion. This paper adds to the evidence base that the link is real and is impressive because it uses semen quality data from more than 30,000 men."

He noted that the paper failed to provide any information on sperm morphology, shape and size, which makes it impossible to determine whether contamination may have caused the sperm to deform and that was why their motility decreased, or if there was some other reason.

From cnBeta.COM