Living with airplanes regularly thundering over your head could risk the healthy pumping of your heart, suggests a new Swiss study.
Based on 4.6 million adults across Switzerland, researchers found that dying from a heart attack was more common with increased exposure to aircraft noise.
"The effect was especially evident for people who were exposed to really high levels of noise, and was dependent on how long those people had lived in the noisy place," said researcher Matthias Egger of the University of Bern.
This isn't the first time that noise has been linked to negative health effects, including cardiovascular risks. But it could be novel progress in determining whether the sound is really exerting the effect, or if it is something else tagging along with the noise, such as air pollution.
High levels of noise and air pollution
"It's been a problem that when you look at road traffic noise there are both high levels of noise and high levels of air pollution," said Egger. "By looking at airports we were in a position to disentangle these effects."
Egger and his colleagues identified 15,532 heart attack deaths among 4.6 million Swiss residents between late 2000 and the end of 2005 using detailed information from an ongoing mortality study called the Swiss National Cohort.
Government records and environmental data helped the team determine the distance of individuals' residences from airports and major roads, as well as relative levels of particulate matter in the vicinity. These allowed the researchers to pinpoint both aircraft noise and air pollution exposures for each individual over a period of 15 years or longer.
Lethal heart attack
After accounting for air pollution and other factors including education and income levels, the group found that both the level and duration of aircraft noise drove up the risk of lethal heart attack.
People exposed to a daily average of at least 60 decibels of noise had a 30% greater risk of dying from a heart attack compared with those exposed to less than 45 decibels, the researchers report in the journal Epidemiology. Among those exposed to the higher decibel levels for 15 or more years, the risk was actually 50% higher.
Measuring exposure is complicated by the fact that aircraft noise is intermittent and can temporarily soar above 100 decibels if you're close to one taking off or landing, explained Egger, but the average of 60 decibels is about what you'd expect in a crowded, noisy bar.
Living within 100 meters of a major road also increased the risk of heart attack. However, the researchers found no impact of particulate-matter air pollution on the heart.
"This adds to growing evidence that there is a causal association between noise exposure and chronic disease, particularly coronary disease," said Hugh Davies of the University of British Columbia School of Environmental Health, in Canada, who was not involved in the study.
Davies pointed to two possible pathways by which noise could harm the body. The first is the well-known fight-or-flight response. "You hear a really loud noise and the first thing you do is jump into the air, literally startled," he said. "We're hard-wired for this response, and it's not something you can easily turn off."
The other path is more indirect: annoyance. Even if something isn't that loud or disturbing, such as a neighbour’s radio, it can become really bothersome if they don't turn it off, he said.
At the end of both routes is the classic stress response, Davies added, which includes a rise in heart rate and blood pressure. Although usually not a problem when it's experienced in short, infrequent bursts, this kind of response can lead to significant wear and tear if it continues daily - as it might if you live on a busy road or under a flight path.
Of course, road and air traffic produce different noise patterns that might not be easily comparable. Road traffic noise is much more constant and arguably easier to get used to than the startling roar of a plane taking off or landing, suggested Egger.
"Noise probably does have effects on health and it is important that we gain a better understanding of these," he said. "Our study can't prove a causal relationship, or be directly generalised. We need further studies."
An earlier study looking at noise exposure during sleep revealed a significant increase in blood pressure from aircraft noise, road traffic and other indoor sources such as snoring.
"This implies that it is the noise itself regardless of the sources that affects the blood pressure," said Jenny Selander of the Karolinska Institute in Stockholm, Sweden, and who was not involved in the study. "I believe that applying these findings to other traffic-related noise sources would be fine."
As the evidence builds, the researchers suggest that further measures should be added to protect people. Sound barriers, controlling the speed and volume of traffic, and better home insulation can all help to reduce exposures, said Egger.
Davies suggested that adjustments to flight paths, cutting back on night flights and improved technology to reduce engine noise could aid in lowering risks as well.
But other than popping in earplugs at night, what is an individual to do? "If this affects you, you could think about moving somewhere quieter. But you'd probably find equal heart benefit if you stopped smoking, ate a healthier diet or exercised more," noted Davies. "There are probably only a few people that noise outright kills."
"In the 1890s, horses and carts on cobble roads in New York City was the big environmental problem," added Davies, noting that a published story at the time expressed excitement over the promise of far quieter horseless carriages. "How far we've come." (Reuters Health/ October 2010)
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