Approximately one in six individuals globally faces infertility issues, and with over half the world’s population residing in urban areas, scientists are investigating whether urban living, with its noise and pollution, contributes to these issues. A recent Danish study utilizing national data has examined infertility, revealing that prolonged exposure to air pollution and traffic noise may be linked to increased infertility, with different effects on men and women. It is established that traffic pollution detrimentally affects the environment and human health, with links to cancer and heart disease. Inhaled pollutants may also reach the reproductive system through the bloodstream, potentially disrupting hormones or directly harming eggs and sperm. While the health impacts of traffic noise are less defined, some studies indicate it may affect stress hormones that influence fertility.
The Danish study utilized comprehensive national registries that track residents throughout their lives using a unique ID number, enabling researchers to connect health information with factors like residence, occupation, education, and family. This method, known as “data linkage,” aims to identify individuals likely attempting to conceive and thus possible recipients of an infertility diagnosis. Over 2 million men and women of reproductive age were identified, with exclusions for those diagnosed with infertility before age 30, individuals living alone or in same-sex partnerships, and those with incomplete data, like a missing address, resulting in 377,850 qualifying women and 526,056 men. Rather than conducting surveys, the study cross-referenced details about these individuals’ residences and an infertility diagnosis over five years using data from the Danish National Patient Register.
Researchers also estimated the exposure level of each residential address to road traffic noise (measured in decibels) and air pollution, specifically fine particulate matter known as PM2.5. Infertility was diagnosed in 16,172 men (out of 526,056) and 22,672 women (out of 377,850). The findings indicated that men exposed to PM2.5 levels 1.6 times above what is recommended by the World Health Organization had a 24% higher infertility risk. Among women, those over 35 exposed to traffic noise 10.2 decibels above the average (55-60 decibels) faced a 14% increased risk of infertility, with similar risks seen regardless of whether they lived in urban or rural areas and even after considering education and income.
The research underscores the potential immediate and long-term reproductive effects of environmental exposure, which may differ based on gender. Men continuously produce sperm after puberty, generating up to 300 million daily, resulting in environmental impacts, such as toxic pollutant exposure, manifesting more quickly on male fertility by affecting sperm count and quality. Women, in contrast, are born with a finite number of eggs and do not produce new ones, though these eggs have mechanisms to mitigate environmental damage over a lifetime. While eggs are not immune to damage, they may exhibit effects over a timeframe longer than the study’s five years. Longer-term studies might reveal similar pollution impacts on women, too. Data linkage, as used in this Danish study, is invaluable for elucidating the effects of environmental exposures on health by enabling analysis across vast populations over extended periods.
However, these studies have limitations, often relying on assumptions when individual surveys or biological factor analyses like hormone levels and body mass are not included. For example, this study assumed couples were actively trying to conceive and gauged exposure to noise and pollution based on residential addresses – assuming individuals were at home. A more detailed understanding could emerge from surveys collecting personal exposure and experience data, including factors like sleep disturbances and stress, known to affect hormone responses and fertility. Hormone-disrupting chemicals are also present at home in everyday household and personal care items.