Tuesday October 12 2010
“Living under a flight path ‘can increase your risk of heart attack’,” reported the Daily Mail. It said, “constant noise from roaring engines can increase the risk by at least 30%”. This Swiss study looked for an association between aeroplane noise, air pollution and the risk of death from heart attack.
The study found that long-term exposure (15 years) to the highest category of plane noise (60db or more) was associated with a 50% increase in the risk of heart attack death, compared to exposure to 45db or less. However, this difference was of only borderline statistical significance, meaning there is a risk that these findings are chance results only.
The 30% increased risk mentioned in the newspaper was based on an analysis that also included people who had been exposed to aeroplane noise for less than 15 years. However, this was not statistically significant, so there is high risk that this is a chance finding.
On its own, this study is not convincing evidence that long-term exposure to aeroplane noise increases the risk of heart attack death. This does not mean there isn’t a link, but further studies would be needed to ascertain this.
Where did the story come from?
The study was carried out by researchers from The University of Bern, Switzerland, and funded by The Swiss National Science Foundation. The research was published in the peer-reviewed journal Epidemiology.
What kind of research was this?
This cohort study investigated whether there was an association between aeroplane noise and air pollution and the risk of death from heart attack.
This type of study can only indicate associations between factors (in this case aeroplane noise and the risk of heart attack). This is the limit of what it can show however, and it cannot prove that aeroplane noise or air pollution themselves increase the risk of heart attack.
What did the research involve?
This study used data from the Swiss National Cohort, which constitutes Swiss national census data combined with their death records and emigration records. The study used data from the December 2000 census, and data on mortality and emigration up to December 2005.
The researchers compared the records of people over the age of 30 who had died of a heart attack with those who had not. They looked at where these people lived and the amount of airline noise they were exposed to (in decibels). Noise exposure during the night as well as the day was also assessed (only the airports of Zurich, Geneva and Basle have air traffic after 10pm).
The researchers also assessed individuals’ levels of exposure to background air pollution concentration, based on how close they lived to major roads. They did this by looking at the number of years people had lived near a busy road, or the number of years they had been exposed to increasing noise levels above 45 decibels. The results were adjusted for gender, socioeconomic and geographical variables, exposure to air pollution and distance to major roads.
What were the basic results?
The researchers analysed data from 4,580,311 people over the five-year study period. During this time, there were 15,532 deaths from heart attack and 282,916 deaths from other causes.
People who had been exposed to aircraft noise of more than 60 decibels or more had a greater risk of dying from a heart attack, compared to those who were typically exposed to less than 45 decibels. The analysis, which only looked at participants who had been exposed to these levels of noise for 15 years or longer, found that people in the noisier environment had a 50% increased risk of heart attack (Hazard ratio [HR] 1.48, 95% confidence interval [CI] 1.01 to 2.18).
There was no association between air pollution (proximity to a major road) and heart attack. There was a small increase in the risk of throat or lung cancer, or stroke for people who had lived within 50 metres of a busy road for 15 years (HR 1.10, 95% CI 1.03 to 1.18 cancer) compared to those who lived more than 200 metres away from a major road.
When the researchers looked at death from any cause, people who lived with aeroplane noise or near a busy road did not have a greater risk of death.
People who lived in areas with higher aeroplane noise or closer to major roads were more likely to be unemployed, less likely to be university educated, more likely have emigrated to Switzerland and more likely to be living in old or unrenovated buildings.
How did the researchers interpret the results?
The researchers say that their study shows that people exposed to high levels of noise from aircraft were at increased risk of dying from heart attack. This association was strongest in those who had lived in the same highly-exposed location for at least 15 years. However, there was little evidence of an association between aircraft noise and all circulatory diseases (such as stroke).
The researchers suggest that exposure to high levels of aircraft noise could lead to increased levels of psychological stress, in turn leading to high blood pressure and heart disease. However, no direct measurements of stress levels or blood pressure were made in this study.
The researchers found that there was a small increased risk of heart attack in people who had been exposed to aeroplane noise of more than 60 decibels for 15 years. However, it should be emphasised that this result was of only borderline statistical significance. Aeroplane noise had no influence on the risk of dying from any other cause.
The researchers attempted to adjust their data for confounding factors that may have influenced the results. For example, they found that the population who lived closer to the Swiss flight paths tended to be of lower socioeconomic status and were less likely to have been to university. It is possible that this may not be the case for the UK population who live along flight paths.
It is important to assess how our environment can affect our health. However, these findings are not robust enough to convincingly show that long-term exposure to aeroplane noise increases the risk of dying from a heart attack. Further studies are necessary to assess whether noise pollution in the UK can affect health.