High levels of air pollution are associated with poor sperm quality and could be partly responsible for the sharp drop in male fertility, according to a new study.

A team of scientists, led by researchers from the Chinese University of Hong Kong, studied the sperm of nearly 6,500 men and found a “strong association” between high levels of fine particulate air pollution and “abnormal sperm shape.”

The report, published in the journal Occupational & Environmental Medicine, said that although the effect is “relatively small in clinical terms” it might still lead to infertility for a “significant number of couples” given the extent of air pollution in cities around the world.

“We found a robust association between exposure to PM2.5 air pollution and low percentage of sperm normal morphology in reproductive-age men,” the researchers wrote.

“Although the effect estimates are small and the significance might be negligible in a clinical setting, this is an important public health challenge.”



Sperm counts among men have more than halved in the last 40 years although scientists are unsure of the cause. Fertility experts greeted the latest research with caution.



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Allan Pacey, professor of andrology at the University of Sheffield, welcomed the report but said that although the findings “may seem quite interesting” the assessment of “sperm size and shape [sperm morphology] is one of the most difficult tests to carry out on sperm and therefore can be less accurate. Moreover, many doctors and scientists now believe that on its own poor sperm morphology is probably not as clinically relevant as we once thought it was.”

Richard Sharpe, an expert in male reproductive health and professor at the University of Edinburgh, said he was “thoroughly underwhelmed” by the findings.



“Sperm morphology is highly variable, both between men and within the ejaculate of an individual man … So changes of the order of magnitude reported here in association with exposure to fine particulate matter are unlikely to be of any great relevance to likely fertility, as the authors admit.”

Sharpe also questioned whether the study had made enough allowance for other factors such as socioeconomic status and diet.

The study looked at 15 to 49-year-old men in Taiwan between 2001 and 2014. It assessed sperm quality and measured the level of fine particulate pollution, which is caused by cars, dust from construction and wood burning, around participants’ homes.

The scientists found a strong association between PM2.5 exposure and abnormal sperm shape. It was associated with a heightened risk of being in the bottom 10% of normal sperm size and shape, after taking account of potential factors, such as smoking and drinking, age and weight.

The study acknowledged that it was unclear how air pollution, which is known to contribute to millions of deaths around the world each year, could impair sperm development. But researchers said many of the components of fine particulate matter, such as heavy metals and polycyclic aromatic hydrocarbons, have been linked to sperm damage in previous experimental studies.



The researchers acknowledged that this was an observational study, so no firm conclusions can be drawn about cause and effect, and they said they were not privy to information on any previous fertility problems of those involved.

But Pacey said it was an important contribution to developing an understanding of the potential causes of male infertility.

“From this and other studies, I remain of the opinion that air pollution probably does have the potential to negatively influence male reproductive health.

“But the jury is still out about quite how and to what extent this impacts on male fertility, rather than measurable and small interesting changes in semen quality.”