A new study in Denmark has utilized nationwide data to investigate the connection between infertility and various factors.
The study found that long-term exposure to air pollution and traffic noise may be linked to increased infertility rates, but the effects differ between men and women.
With over half of the global population now residing in urban areas, researchers are investigating whether living in noisy, polluted cities might be a contributing factor.
Traffic pollution's harmful impact on the environment is undeniable. Its negative effects on human health are also well documented, with established links to conditions such as cancer and heart disease.
Chemicals inhaled from polluted air may also travel to the reproductive tract via the blood. This can reduce fertility by either disrupting hormone levels or directly damaging eggs and sperm.
The effects of traffic noise on health are less understood, but some research suggests that it affects stress hormones, potentially altering the fertility.
This new study was conducted in Denmark, where data on every resident is collected throughout their lifetime using a unique identification number, allowing for comprehensive analysis across multiple national databases.
Nationwide data allows researchers to investigate links between a person’s health and factors such as where they live, their job, education history and family. This method is called “data linkage”.
The study aimed to capture individuals who were likely trying to conceive and, therefore, at risk of being diagnosed with infertility
The study identified over 2 million men and women of reproductive age, specifically those who were:
- Aged 30 to 45
- Living together or married
- With fewer than two children
- Residing in Denmark between January 1, 2000, and December 31, 2017
The study excludes every individual diagnosed with infertility before age 30, those living alone or in a registered same-sex partnership, and anyone with incomplete information, such as missing addresses.
There were 377,850 women and 526,056 men who fit these criteria.
Instead of surveying participants, the study cross-checked detailed information about their residence and infertility diagnoses over a five-year period using data from the Danish National Patient Register.
Researchers estimated the level of exposure to road traffic noise (measured in decibels) and air pollution, specifically the concentration of fine particulate matter (PM2.5), for each residential address.
16,172 men (out of 526,056) and 22,672 women (out of 377,850) were diagnosed with infertility
The study found that men exposed to PM2.5 levels 1.6 times higher than the World Health Organization's recommendations faced a 24% increased risk of infertility.
For women over 35, exposure to traffic noise at levels 10.2 decibels higher than average (55-60 decibels) was associated with a 14% increased infertility risk.
The risks were comparable regardless of whether individuals lived in urban or rural areas and remained consistent when accounting for education and income.
The study highlights about the effects of environmental exposure on reproductive health, with differing impacts on male and female fertility for both immediate and long-term effects.
After puberty, men continuously produce sperm—up to 300 million a day.
The environmental changes, such as exposure to toxic pollutants, can impact male fertility more quickly than female fertility, affecting both sperm count and quality.
In contrast, women are born with all their eggs and cannot produce new ones. These eggs have built-in "damage control" mechanisms to protect them from environmental hazards throughout a woman's lifetime.
This doesn't mean eggs are immune or cannot get damaged, but the effects may take longer than the five years of exposure examined in this study to become evident. Longer-term studies might reveal similar impacts of pollution on women's fertility.
Data linkage is a powerful tool for uncovering links between environmental exposures and health. It enables the assessment of large populations over extended periods, as demonstrated by this recent Danish study.
However, there are inherent limitations to these types of studies. Without directly surveying individuals or examining biological factors such as hormone levels and body mass, the research relies on certain assumptions.
For example, this study involved significant assumptions about whether couples were trying to conceive. Additionally, it calculated individuals' exposure to noise and air pollution based on their addresses, assuming they spent most of their time at home.
A more accurate picture could be obtained by gathering individual-specific information about their exposure levels and experiences, including details related to fertility.
For instance, surveys could include factors such as sleep disturbances and stress, which can affect hormone responses and impact fertility. Additionally, exposure to chemicals that disrupt hormones, often found in household and personal care products, could be considered.
This study is unprecedented in its scale and represents useful step in exploring the potential link between air pollution, traffic noise, and infertility
However, more controlled studies with actual measures of exposure, rather than estimations, are needed to deepen our understanding of how these factors impact both men and women.
Reference:
1. Sørensen, Mette, Aslak Harbo Poulsen, Bugge Nøhr, Jibran Khan, Matthias Ketzel, Jørgen Brandt, Ole Raaschou-Nielsen, and Allan Jensen. “Long term exposure to road traffic noise and air pollution and risk of infertility in men and women: nationwide Danish cohort study.” BMJ, September 4, 2024, e080664. https://doi.org/10.1136/bmj-2024-080664.
(Inputs from various sources)
(Rehash/Simran Sethi/MSM)
