Wednesday October 9 2013
Aircraft noise can exceed 63 decibels during the day
“Living near an airport may increase your chances of dying from stroke, heart and circulatory disease,” The Daily Mail reports.
Researchers have compared data on daytime and night-time aircraft noise with hospital admissions and death rates among 3.6 million people living near London's Heathrow airport.
They found that risks of hospital admission and death from stroke, heart and cardiovascular diseases are between 10 and 25 per cent higher in areas with high levels of aircraft noise.
With arguments raging about the proposed expansion of Heathrow and other airports to increase UK flight capacity, the possible impact of aircraft noise on health is an important topic for research.
However, the results of this large study should be viewed with caution. As the authors point out, they were unable to take account of individual factors which might affect the risk of these diseases such as diet, smoking, lack of exercise and other medical disorders.
Where did the story come from?
The study was carried out by researchers from the several UK institutions. It was funded by Public Health England, the UK Medical Research Council and the European Network for Noise and Health.
The study was published in the peer-reviewed British Medical Journal.
A further study published in the BMJ looked at whether exposure to aircraft noise increases the risk of hospitalisation for cardiovascular diseases in people of 65 or older living near airports. The US study found a 3.5% higher hospital admission rate in areas with higher aircraft noise. However we have not examined this study in detail here.
The UK study was covered fairly in the papers. The Guardian correctly pointed out that researchers had found a preliminary link but not proof that high aircraft noise levels cause disease.
What kind of research was this?
In this study, researchers investigated the association of aircraft noise with risk of stroke, coronary heart disease, and cardiovascular disease in the general population. It is known as a small area study, which means that the area covered – 12 London boroughs and nine districts outside London – was divided into more than 12,000 small areas each with a population of about 300.
The researchers say that few studies have examined aircraft noise and the risk of heart disease or stroke, although some previous research has found an increased risk of high blood pressure associated with aircraft noise and a higher risk of high blood pressure, stroke, and coronary heart disease associated with road traffic noise. There is also evidence of a link between these diseases and noise exposure at work, and of short term effects of noise on the cardiovascular system.
Heathrow airport, situated in a densely populated area in west London, is one of the busiest airports in the world.
What did the research involve?
The researchers’ study area covered 12 London boroughs and nine districts west of London, which are exposed to aircraft noise, defined as exceeding 50 decibels (about the volume of a normal conversation in a quiet room). The data was supplied by the Civil Aviation Authority.
Using information from the national census, they divided the area into 12,110 small areas (or neighbourhoods) each with a population averaging 297. They also divided the area into 2,378 larger (or super output) areas of 1,510 inhabitants.
Using detailed noise data from the Civil Aviation Authority they calculated the annual average noise levels for both daytime and night-time aircraft noise for both the smaller and larger areas. Daytime noise was defined as 7am to 11 pm, night-time noise as 11pm to 7am.
The researchers grouped daytime aircraft noise and road noise into six categories, from 51 decibels (dB) or less, to more than 63dB, in increments of 3dB (3dB represents a doubling in sound intensity that is just perceptible as a change in loudness to the human ear). For aircraft noise, 57dB is taken as the point at which “noticeable community annoyance” starts to occur, and the aircraft noise categories included a 57dB cut off point.
For night-time aircraft noise (which affected fewer areas), the researchers used three dB categories, in increments of 5dB (50dB or less, 50-55dB and more than 55dB).
The researchers then obtained data on hospital admissions (including the main reason for admission and the first episode of stay in a given year) and deaths (by the underlying cause) for the study area from 2001-05, using official information from the Office for National Statistics and the Department of Health.
Using international coding, they collected data on both admissions and deaths for stroke, coronary heart disease and cardiovascular disease. They linked hospital admissions for these diseases by postcode (average 23 households) to the small area, and deaths from these diseases to the larger (super output) area.
For all areas, they collected official data on ethnic composition, social deprivation and lung cancer rates (which is a proxy measure for the prevalence of smoking). These are factors (confounders) which might affect rates of heart disease and stroke. For the 12 London boroughs they also obtained data on two further possible confounders – air pollution and daytime noise from road traffic.
The researchers analysed the association between aircraft noise, hospital admissions and deaths from coronary heart disease, stroke and cardiovascular disease. They adjusted their results for age, sex, ethnicity, deprivation and lung cancer rates (the proxy for smoking). For the 12 London boroughs they also adjusted findings for air pollution and road noise.
What were the results?
The researchers found that the risk of hospital admissions for these diseases increased in line with increasing levels of daytime and night-time aircraft noise.
When areas experiencing the highest levels of daytime aircraft noise were compared with those experiencing the lowest levels, the risk of hospital admission was:
- 24% higher for stroke (relative risk 1.24, 95% confidence interval 1.08 to 1.43)
- 21% higher for coronary heart disease (RR 1.21, CI 1.12 to 1.31)
- 14% higher for cardiovascular disease (RR 1.14, CI 1.08 to 1.20)
The researchers say that the higher risks for deaths from these disorders were of a similar magnitude, although with wider confidence intervals. They also point out that admissions for coronary heart disease and cardiovascular disease were particularly affected by adjustment for south Asian ethnicity, which is a risk factor for these disorders.
None of the results were affected by adjustment for air pollution, and road traffic noise in the London boroughs.
The researchers say they could not distinguish between the possible effects of daytime or night-time noise as both these were “highly correlated” – which means that areas with highest daytime aircraft noise also had highest night-time noise.
How did the researchers interpret the results?
The researchers say their results suggest that high levels of aircraft noise were associated with increased risks of stroke, coronary heart disease, and cardiovascular disease, but that further work to understand the possible health effects of aircraft noise is needed. Acute exposure to noise has been found to raise blood pressure, a major risk factor for stroke and heart disease they point out. It could affect the neuroendocrine system thereby raising stress hormone levels.
Policy decision on aircraft capacity needs to take account of potential health related concerns, they argue.
With debate currently taking place about the expansion of airports around London, the possible effects of aircraft noise on health is an important area for research. But as the authors point out, this study has several limitations. In particular, although the authors took account of confounders such as ethnicity, deprivation and smoking rates at the area level, they had no information on these factors at the individual level. So results at area level are not applicable to all individuals within these small areas.
In addition, the risk of coronary heart disease may have been affected by large south Asian populations, since south Asian ethnicity is associated with a higher risk of heart disease. It is possible that this or other factors that they were unable to adjust for could be affecting the link, however the researchers seem to have adjusted for the major known risk factors for heart disease and stroke.
A further source of bias is that the authors had no access to migration in and out of the study areas.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.