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Clinical Articles, Lead Article

Road traffic noise linked to deaths and increased risk of stroke

Long-term exposure to road traffic noise is associated with small increased risks of all-cause mortality and cardiovascular mortality and morbidity in the general population, particularly for stroke in the elderly, according to a recent UK study.1

The study population consisted of 8.6 million inhabitants of London. The researchers assessed small-area-level associations of day- (7:00–22:59) and night-time (23:00–06:59) road traffic noise with cardiovascular hospital admissions and all-cause and cardiovascular mortality in all adults (≥25 years) and elderly (≥75 years) through Poisson regression models.

They adjusted models for age, sex, area-level socioeconomic deprivation, ethnicity, smoking, air pollution, and neighbourhood spatial structure. Median daytime exposure to road traffic noise was 55.6 dB. Daytime road traffic noise increased the risk of hospital admission for stroke with relative risk (RR) 1.05 [95% confidence interval (CI): 1.02–1.09] in adults, and 1.09 (95% CI: 1.04–1.14) in the elderly in areas >60 vs. <55 dB.

Night-time noise was associated with stroke admissions only among the elderly. Daytime noise was significantly associated with all-cause mortality in adults [RR 1.04 (95% CI: 1.00–1.07) in areas >60 vs. <55 dB]. Positive but non-significant associations were seen with mortality for cardiovascular and ischaemic heart disease, and stroke. Results were similar for the elderly.

Dr Jaana I Halonen (London School of Hygiene and Tropical Medicine)

Dr Jaana I Halonen (London School of Hygiene and Tropical Medicine)

Speaking to BJC Arrhythmia Watch, lead author, Dr Jaana I Halonen, research fellow at London School of Hygiene and Tropical Medicine (2014) and Finnish Institute of Occupational Health (2015– ), said:

The population attributable fraction, that is, the proportion of events that would be avoided if daytime middle (55–60dB) and high (>60dB) exposures were replaced with the reference level exposure (<55dB) was 2.5% (range 0.7%–4.2%) for all-cause mortality among adults aged 25 years or more. Among the elderly (≥75 years), the corresponding population attributable fraction regarding all deaths was 2.5% (range 0.7%–4.3%).

For stroke admissions among the elderly, this calculation results in 5.2% (range 2.5%–7.8%) of events that would be avoided if daytime middle (55–60dB) and high (>60dB) exposures were replaced with the reference level exposure (<55dB).

However, it should be noticed that we didn’t have full information in this type of (ecological) study on all factors that might affect an individual’s risk of dying or being hospitalised such as smoking, medical history, exercise levels, occupation etc., and replication of our findings in large individual-level studies with more detailed information on exposure modifiers and confounders is needed.

The noise levels are shown in the noise map (see figure 1). Of the Lower Layer Super Output Areas (LSOA) the highest noise levels were found in Bromley 039B, Greenwich 022D and Havering 005B. Please note that LSOAs don’t have unique names, locations are specific only in connection with the four digit code.

Figure 1. Map indicating noise levels

Figure 1. Map indicating noise levels

Exposure to day- or night-time noise may have an indirect pathway through the autonomic nervous system increasing heart rate, blood pressure, and concentrations of noradrenaline ( a potential stress hormone). Noise can also affect the hypothalamus–pituitary–adrenal axis leading to increased levels of cortisol, another stress hormone. In the long term, these reactions are suggested to promote low-grade inflammation and cardiovascular morbidity.

For night-time noise, another, suggested (direct) pathway is via sleep disturbance that can increase the level of stress hormones and thus to promote low-grade inflammation and cardiovascular morbidity.

We had limited information on individual-level confounders. We adjusted for area-level deprivation, which is linked to individual-level socioeconomic status and a general marker of social conditions. Data on personal stressors was not available in the administrative datasets used in the study.

The role that noise exposure may play in ill health is not well understood and needs further study before being able to make these type of recommendations.  Our study examined the average risks in areas, but this is not the same as the risk for an individual as individual circumstances will differ. Also, we did not have information on migration in this study and it may be that the elderly have lived in the same place for longer, therefore we might have had less exposure misclassification when estimating older peoples’ risks from noise.

The size of the risks we detected were much smaller than the well-established individual-level risk factors for stroke, heart and cardiovascular disease such as smoking, obesity, low levels of exercise and an unhealthy diet or medical conditions such as diabetes, high blood pressure and high cholesterol (especially if untreated). These factors are likely to be the most important determinants of disease risk.

We would advise anyone concerned about their risk of stroke or heart disease to discuss with their family doctor.

References

1. Halonen JI, Hansell AL, Gulliver J, et al. Road traffic noise is associated with increased cardiovascular morbidity and mortality and all-cause mortality in London. Eur Heart J 2015;36:2653–61. http://dx.doi.org/10.1093/eurheartj/ehv216

Published on: November 24, 2015

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