Chronic exposure to high levels of airplane noise is associated with an increased risk of developing cardiovascular disease, particularly for older people, according to two new studies published online Tuesday in the journal BMJ.

For one of the studies, researchers examined data on airplane noise and hospital admissions around London Heathrow Airport. For the other, a separate team of researchers pooled and analyzed similar data for multiple U.S. airports.

The Minneapolis-St. Paul International Airport is included in that second study. These findings, therefore, are likely to fuel the controversy surrounding the Metropolitan Airport Commission’s plans to concentrate air traffic over particular neighborhoods of Southwest Minneapolis, Edina and Richfield.

Past research

Previous studies have found an association between airplane noise and an increased risk of sleep problems, anxiety and high blood pressure. But most of that research focused on only a small number of airports or didn’t have sufficient statistical power to strongly support their results. These two new studies are better powered, statistically speaking, than the earlier ones. They also do a better job of adjusting for confounding factors, such as air pollution.

Most important, the new studies investigated the relationship between airplane noise and the incidence of cardiovascular disease, not just the incidence of high blood pressure.

Neither study proves that airplane noise causes heart disease, however. These are observational studies. They can show only a correlation, not a cause-and-effect relationship, between two things (in this case, airplane noise and heart disease). Other factors, not yet identified and measured, might very well explain both studies’ findings.

The U.S. study

In the larger of the two studies, researchers from Harvard University and Boston University examined 2009 data for more than 6 million Medicare recipients (aged 65 years or older) living near 89 U.S. airports. First, they matched hospitalizations records for cardiovascular illnesses (such as heart failure, stroke, peripheral vascular disease and heart-rhythm disturbances) with the patients’ ZIP codes. Next, with the aid of Federal Aviation Administration data, they determined the airplane-related noise levels of each zipcode.

The researchers then looked to see if there was a relationship between level of noise and the hospitalizations.

“In our analysis, we found that even when controlling for air pollution, proximity to roadways, individual demographics and socioeconomic status, a 10 decimal increase in noise was associated with a 3.5 percent increase in cardiovascular hospital admissions — and this was statistically significant,” said Jonathan Levy, one of the study’s co-authors and a professor of environmental health at Boston University, in a video released with the study.

The analysis also revealed that the strongest association with cardiovascular-disease hospitalizations occurred among the participants exposed to the highest noise levels (more than 55 decibels). (According to the National Institutes of Health, 55 decibels is about the sound of a normal conversation.)

Overall, said Levy, “about 2.3 percent of the cardiovascular hospital admissions were associated with aircraft noise.”

The U.K. study

In the second study, a team of British researchers compared airplane noise with cardiovascular-related hospital admissions among 3.6 million people living near London Heathrow Airport, one of the busiest airports in the world.

They found that people living in the areas around Heathrow with the most airplane noise (63 decibels in the daytime or more than 55 decibels at night) were 20 to 30 percent more likely to be hospitalized for stroke and heart disease than those living in areas with the lowest levels of noise.

The findings remained significant even after adjusting for income levels, ethnicity, smoking (estimated through lung cancer mortality), air pollution and exposure to road-traffic noise.

The researchers were not able, however, to distinguish between daytime and nighttime airplane noise. They called for more studies to help determine if the correlation between airplane noise and heart disease could be the result of sleep disruption.

Important implications

Although both studies may have found an association between high levels of airplane noise and an increased risk of cardiovascular illness, the increased risk is much smaller than that from other established risk factors, such as smoking, high blood pressure, diabetes and obesity.

But that doesn’t mean that the effects of airplane and other environmental noises on human health are negligible.

“Environmental noise is an understudied environmental pollutant that has important implications for public health and policy,” writes Dr. Stephen Stansfeld, a professor of psychiatry at the Queen Mary University of London, in a BMJ commentary that accompanies the published studies.

“These studies,” he adds, “provide preliminary evidence that aircraft noise exposure is not just a cause of annoyance, sleep disturbance, and reduced quality of life but may also increase morbidity and mortality from cardiovascular disease. The results imply that the siting of airports and consequent exposure to aircraft noise may have direct effects on the health of the surrounding population. Planners need to take this into account when expanding airports in heavily populated areas or planning new airports.”

The studies and the editorial can be read on the BMJ website.