Male and female infertility impacted by different pollution types

A new nationwide study in Denmark has linked infertility to different types of pollution with differences between men and women.

Men exposed to air pollution over an average of five years had a higher risk of infertility, according to a large new Danish study which adds to an increasing body of evidence about the impact of fine particulate matter on fertility.
The new nationwide study, published in the British Medical Journal (BMJ) on Wednesday, also found a link between noise pollution and infertility among women aged between 35 and 45, an association that had not previously been known.
Noise pollution was also weakly linked to infertility among men aged 37 to 45, researchers said.
Based on data from all Denmark residents, the study population included men and women aged 30 to 45 who were cohabiting or married with fewer than two children between 2000 and 2017. 
It was designed to include a “high proportion of people actively trying to achieve pregnancy,” with the final study population having more than 377,000 women and 526,000 men. 
Of those, roughly 16,000 men and 22,600 women in that group received an infertility diagnosis. 
Individuals with a prior infertility diagnosis or people who had undergone surgery to prevent them from having children were excluded from the study group.
The findings linking different pollution types to a higher risk of infertility were consistent across different socioeconomic groups and people living in suburban, urban, and rural areas.
“As many Western countries are facing declining birth rates and increasing maternal age at the birth of a first child, knowledge on environmental pollutants affecting fertility is crucial,” the study authors said.
The study focused on long-term exposure to road traffic noise and particle pollution, or PM2.5, such as car exhausts and power plant smoke in the Danish population.
Previous research has found that this type of air pollution is linked to lower sperm quality, in particular to sperm motility and counts.
These two types of pollution are “the most frequent pollutants in urban environments, so for us, it seemed logical to start there and look at these two major pollutants in our daily life,” Mette Sørensen, the first author of the study and a senior scientist at the Danish Cancer Society, told Euronews Health.
She added that they focused on noise pollution since it is known to impact stress and sleep and affect “other diseases like cardiovascular disease and diabetes”.
“Our hypothesis was that if you are stressed, if you’re disturbed by sleep, then it could also impact infertility,” Sørensen said.
The researchers were able to access Danish addresses using the civil registration system and then used mathematical models to estimate the particle pollution based on nearby cars or ships and acoustic models to estimate noise pollution.
“While the research is commendable, certain estimations and assumptions were necessary, such as road traffic noise and pollution levels, and the study could not account for environmental exposure outside the home, like in the workplace,” Alison Campbell, chief scientific officer at Care Fertility and an honorary professor at the University of Kent in the UK, said in a statement.
“Although noise has not been widely studied in relation to fertility, there is evidence suggesting a link between noise-induced stress and sleep disturbance, which could impact fertility,” Campbell, who was not involved in the study, added.
“Previous studies have already shown air pollution affects sperm quality, though evidence regarding its impact on female fertility is mixed, highlighting the need for further research in this area”.
Sørensen said one of the interesting findings of their study was that there was no lower threshold or lower level at which these pollutants were not harmful to the Danish population.
The study was observational, so it did not determine a causal relationship between pollution and infertility.
But if the findings are confirmed in future studies, the researchers concluded, “it suggests that political implementation of air pollution and noise mitigations may be important tools for improving birth rates in the Western world”.