Researchers in Shanghai studied 33,876 men in China and found that those who lived in areas with higher levels of particulate matter in the air tended to have worse sperm quality, especially in regards to sperm motility – the ability of the sperm to swim the right way.
Particulate matter (or PM) is the term often used in the study of air pollution to describe tiny solid particles and liquid droplets found in the air, whether it be dust, dirt, soot, or smoke. The particulate matter isn’t invisible to the naked eye and it's known that smaller specks of air pollution are especially dangerous because they are able to go deep into the lungs and make their way into the bloodstream.
This is something the new study from China picked up on, showing that declines in sperm quality were particularly noticeable in people who had been exposed to smaller molecules of particulate matter.
“Our findings suggest that smaller particulate matter size fractions may be more potent than larger fractions in inducing poor sperm motility,” the study reads.
It’s hardly Earth-shattering news to hear that air pollution isn’t good for your health – previous research has linked poor air quality to everything from cardiovascular problems and dementia to autism and vision loss.
However, the link between sperm quality and polluted air has never been conclusively shown due to inconsistent data. Other experts in the field still say the link is not definitely proven, but this latest evidence is pretty convincing.
“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,” commented Professor Allan Pacey, Professor of Andrology at the University of Sheffield.
“The conclusions (that increased air pollution in this particular part of China may be associated with reduced sperm motility) is interesting but of course is correlation and not causation,” added Pacey.
It’s also worth noting that factors other than air quality may be at play here. Factors that influence sperm quality like ethnicity, age, body mass index, smoking, alcohol consumption, and some aspects of the weather were taken into account by the researchers, but it’s not possible to adjust for everything that might have been relevant.
Based on these limitations, some researchers say the findings – although important and interesting – need to be taken with some caution.
“They mention that they didn’t adjust for dietary habits and physical condition, and I’d add that they didn’t adjust for the men’s occupations (though they did adjust for educational level, which would be related to occupation to some extent). Therefore they really can’t (and don’t) conclude that this study has shown that particulate air pollution causes issues with sperm motility,” explained Professor Kevin McConway, Emeritus Professor of Applied Statistics at the Open University.