Long-term exposure to air pollution is linked to a higher risk of infertility in men, while prolonged exposure to road traffic noise is associated with a higher infertility risk in women, a recent study found.
The peer-reviewed Danish study, published Wednesday in the BMJ, said exposure to fine particulate matter (PM2.5) was linked to a greater likelihood of an infertility diagnosis in men, independent of age. Meanwhile, road traffic noise showed a similar association with infertility in women over 35 and potentially in men over 37.
If these results are confirmed in future studies, higher fertility could be added to the list of health benefits from regulating noise and air pollution, the Danish researchers argued.
“We already know that noise and air pollution are linked to other diseases like cardiovascular diseases and diabetes for example. So if we can add infertility to this, it is a better argument for doing something and against these things,” said Allan Jensen, senior author of the study and senior researcher at the Danish Cancer Institute.
Although the study was conducted in Denmark, he noted that similar results are likely to be seen in other major cities in Western countries, including Canada.
In Canada, one in six adults will be impacted by infertility in their lifetime, according to Fertility Canada.
In 2022, Canada’s fertility rate reached its lowest level on record, at 1.33 children per woman (compared to 1.41 in 2021). The drop in fertility rate in 2022 was not unique to Canada, although the country’s decrease was one of the largest among high-income countries.
Apart from the United States, all G7 countries experienced a fertility decline between 2021 and 2022, Statistics Canada reported.
Infertility in both men and women is linked to a range of long-term health problems, such as a shorter life expectancy and a higher risk of psychiatric disorders and other physical diseases, the authors of the study argue.
Carolynn Dubé, the executive director of Fertility Matters Canada told Global News that infertility can cause significant physical, mental and financial strain on people.
“People who are experiencing infertility or who need to use fertility care to build their families experience incredibly high rates of stress, depression and anxiety. And it really takes a toll on their mental health. In fact, a diagnosis of infertility has the same impact on someone’s mental health as being diagnosed with a more significant health disease like cancer, but [we] don’t treat it the same,” she told Global News.
Dubé added that timing can be another compounding factor when it comes to fertility.
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“The reality is we have a biological clock, and we do know that males and people with testicles also have a biological clock. It’s just that the ovaries are at more of a disadvantage,” she said.
The researchers examined Denmark’s national registry data for more than 526,000 men and 377,000 women aged 30 to 45 years, with fewer than two children, cohabiting or married between 2000 and 2017.
Individuals with an existing infertility diagnosis were excluded, as were women who had undergone surgery that prevents pregnancy and men who were sterilized.
Yearly average PM2.5 concentrations and road traffic noise levels at each participant’s address were calculated, and infertility diagnoses were recorded from the national patient register.
Infertility was diagnosed in 16,172 men and 22,672 women during an 18-year follow-up period. After adjusting for several potentially influential factors including income, education level and occupation, exposure to higher average levels of PM2.5 over five years was associated with a 24 per cent increased risk of infertility in men aged 30 to 45 years. PM2.5 was not associated with infertility in women.
Exposure to higher average levels of road traffic noise over five years was associated with a 14 per cent increased risk of infertility among women older than 35 years.
Noise was not associated with infertility among younger women (30 to 35 years).
In men, road traffic noise was associated with a small increased risk of infertility in the 37 to 45 age group, but not among those aged 30 to 37 years.
What is causing the link?
Jensen emphasized the need for further studies to identify the biological factors that may be driving this link.
“This is an epidemiologic study. It’s based on the Nordic registries, which are very good. So we can link a lot of information, but we cannot say that this is a causal finding,” he said.
But there may be theories explaining the association between infertility and pollution.
“So if we start with air pollution and men, what we think is [happening], is you inhale the very small particles, and then these very small and tiny particles can transfer from the air from the lung tissue into the bloodstream. And then they can have a direct toxic effect on the sperm cells.”
And some studies have looked into this theory.
A 2023 study published in Front Public Health found that exposure to PM2.5 was associated with a decreased total sperm count, based on a systematic review and meta-analysis involving 93,996 Chinese men.
For women, the study found that air pollution did not have an impact on fertility, but road noise did — such as car horns and construction.
“It may sound a little odd that noise can cause infertility, but we hypothesize that noise induces stress and also problems sleeping,” Jensen said.
“In women above 35 years of age, the fertility has already started to drop, and many women know this, so they are already in this state of distress. And then if they are exposed to even more stress and sleeping disturbances from noise, it can simply tip over so that we see that it is a risk factor for the older women, but not for the younger ones.”
According to the World Health Organization (WHO), the health impacts of environmental noise are a growing concern, due to including cardiovascular disease, cognitive impairment, sleep disturbance and tinnitus.
Although the study is observational, Dubé said if anyone is worried about their fertility and hoping to conceive it is best to talk with their physical or contact Fertility Matters Canada for more details.