Living in areas with road traffic noise above 60 dB has been linked to greater risk of all-cause mortality and stroke.
According to the World Health Organization (WHO), daytime community noise can be harmful to human health when it reaches above 55 decibels (dB). Millions of people living in urban areas around the world, however, are exposed to daytime noise well above this level.
A 2014 study published in Environmental Health Perspectives estimated that around 104 million Americans - around 50% of the US population - have annual exposures to traffic noise at levels above 70 dB.
As well as increasing the risk of hearing impairment, exposure to loud noise has been linked to numerous other health problems. In October 2013, for example, a study associated noise from aircrafts to greater risk of cardiovascular disease, while a more recent study linked noise pollution with increased waist size.
Now, Dr. Jaana Halonen, of the London School of Hygiene & Tropical Medicine in the UK, and colleagues have added to the list of noise-associated health risks, finding long-term exposure to noise from road traffic may reduce mortality and increase stroke risk.
To reach their findings, Dr. Halonen and colleagues investigated how long-term exposure to road traffic noise impacted hospital admissions and life expectancy among 8.6 million people living in London between 2003 and 2010.
Using the TRAffic Noise EXposure (TRANEX) model, the team assessed levels of daytime road traffic noise (7am - 11pm) over different areas of the city, as well as levels of nighttime road traffic noise (11pm - 7 am).
The researchers then compared this information with the number of deaths and hospital admissions that occurred in 2003-10 among individuals aged 25-74 and 75 and older.
Road traffic noise above 60 dB linked to 4% greater risk of all-cause mortality
During the study period, the researchers identified 442,560 deaths from all causes, of which 291,139 occurred among elderly individuals. Cardiovascular problems were the cause of hospital admission for 400,494 adults between 2003-10, of whom 179,163 were elderly.
Compared with individuals who lived in areas where road traffic noise levels were below 55 dB, those who lived in areas where road traffic noise reached above 60 dB were found to be at 4% greater risk of all-cause mortality.
Dr. Halonen and colleagues say this increased risk death is most likely due to cardiovascular problems that have been triggered by increased blood pressure, stress and sleep problems as a result of road traffic noise.
The researchers also found that adults aged 25-74 who lived in areas where traffic noise was above 60 dB were at 5% greater risk of stroke, while the risk was even higher for elderly adults, at 9%.
Nighttime road traffic noise at 55-60 dB was also associated with a 5% increased stroke risk among elderly individuals, though nighttime road traffic noise was not linked to greater stroke risk among younger adults.
Commenting on their findings, the researchers say:
"This is the largest study to date to investigate environmental noise and cardiovascular disease in the general population. Results suggested small increased population risks of all-cause mortality and cardiovascular mortality and morbidity, particularly of stroke in the elderly, at moderate levels of road noise exposure. Findings are consistent with the larger body of evidence linking traffic noise exposure with hypertension."
The team notes that their findings may not apply to people on an individual level, explaining that they were unable to adjust the results for individual-level confounders, such as health behaviors, socioeconomic status and other cardiovascular risk factors.
Still, the study supports previous research suggesting that long-term exposure to road traffic noise may negatively impact health.