To establish the quality of the semen, the researchers zeroed in on factors such as sperm count, concentration, and sperm motility. Photograph: Roman Kybus/Getty Images/iStockphoto
Air pollution may affect semen quality, specifically sperm motility — the ability of sperm to swim in the right direction — according to a new study analysing the sperm of over 30,000 men in China.
The research, published today in the journal JAMA Networks, also suggests that the smaller the size of the polluting particles in the air, the greater the link with poor semen quality.
“Our findings suggest that smaller particulate matter size fractions may be more potent than larger fractions in inducing poor sperm motility,” wrote the authors of the paper. The researchers believe that these findings highlight yet another reason for the need to reduce exposure to air pollution among men in their reproductive age.
Researchers have long been trying to establish whether there’s a link between air pollution and sperm quality, but it’s been unclear whether the former has adverse health effects on male fertility because the results from studies are often inconsistent among themselves and complicated to put into perspective. There does appear to be reason to believe that pollution may negatively affect fertility in general for the whole of the population, as suggested in this international literature review published in December 2021.
Researchers at the School of Medicine of Tongji University in Shanghai looked at data records from a total of 33,876 men from 340 Chinese cities, aged 34 on average, with a varied degree of exposure to air pollution among them, and whose wives got pregnant through assisted reproduction technology with their sperm between January 2013 and December 2019.
They then looked for patterns between semen quality in relation to whether the participants had been exposed to amounts of particulate matter smaller in diameter than 2.5 micrometres, between 2.5 and 10 micrometres, and 10 micrometres, in various key moments of the 90 days before their visit to the hospital for semen ejaculation. To establish the quality of the semen, the researchers concentrated on factors such as sperm count, concentration, and sperm motility.
Although the researchers couldn’t find a significant link between air pollution and sperm quality in terms of sperm count or concentration — they did find that the more a participant was exposed to smaller particulate matter, the lower both the progressive and the total sperm motility was. Progressive sperm motility is the sperm’s ability to swim forward, while total sperm motility simply refers to the sperm’s ability to swim in general.
Specifically, when exposed to particulate matter smaller in diameter than 2.5 micrometres. there was an estimated decrease in sperm motility of 3.6%, while when exposed to particulate matter of 10 micrometres in diameter, there was 2.44% less sperm motility. Meaning that it’s possible that different size fractions of particulate matter might have differing effects on semen quality, maybe because the smaller the particulate matter, the more likely it is to travel deeper into the human lungs.
The data indicates that the effects of pollution are more prominent when exposure takes place during the initial part of the 90 days of sperm creation — the one called spermatogenesis — rather than the other two phases. This, in turn, may mean that particulate matter affects sperm on a genetic level, according to the researchers, but these are just speculations, and there’s more research to be done in this area.
“The possibility of a link between air pollution and semen quality has been suggested in a number of studies over the years, although not all of them have agreed with this conclusion,” said Allan Pacey, professor of andrology at the University of Sheffield, who was not involved in the research. “This paper adds to the evidence base suggesting the link is real, and is impressive because it uses semen quality data from over 30,000 men.”
“But the level of decline in sperm motility seems to be quite low,” said Pacey, stressing that correlation is not causation. He noted that the paper failed to provide any information about the morphology, shape and size of the sperm, which made it impossible to determine whether pollution might be responsible for deformation of sperm and that’s why their motility is decreased, or whether there were other reasons.
According to Pacey, it is important to take these findings with a pinch of salt. Although the data suggests that pollution may have a negative effect on sperm mobility, there still isn’t enough information to infer whether this can have a significant clinical effect at large, and result in the overall decrease of the ability of men in high pollution areas to become fathers. More research out in the field might help answer that question with more certainty in the future.