Road Traffic Noise - Factors modifying its relation to annoyance and cardiovascular disease

Abstract: Traffic noise causes annoyance and sleep disturbance and has been linked with several other adverse effects on life quality and health, including increased risk of hypertension and myocardial infarction. Conservative estimates assume that at least one million healthy life years are lost every year from traffic related noise in the western part of Europe. We know from earlier studies that the adverse effects of environmental noise may be modified by social, demographic and individual factors. However, there is a need to better evaluate exposure-response in susceptible groups. The aim of this thesis was to test a number of factors hypothesised to modify the association between road traffic noise, annoyance and cardiovascular disease. Paper I-III are cross-sectional, while paper IV is a cohort study. The four different study populations in this thesis were selected through stratified random sampling of men and women aged 18-80 years old in the county of Skåne and its major city Malmö in southern Sweden. Exposures of road traffic and railway noise as well as air pollution were modelled using geographic information system (GIS) for the survey participants’ residential addresses. Possible confounding and modifying factors were mainly drawn from survey responses while outcomes were based on both self-reporting and inpatient registers. We were not able to show a relation between current and medium-term noise exposure to road traffic noise and incident myocardial infarction or ischemic heart disease in the general population. Air-pollution at low levels did not modify this effect. An association was however found between road traffic noise and hypertension in a cross-sectional study >60dB(A). We also found strong and positive relations between road traffic noise and annoyance. Railway noise was found to be less annoying at intermediate levels, but not >55dB(A). Access to quiet side had a protective effect and decreased the risk of annoyance, sleep and concentration problems equal to a 5dB(A) decrease in noise exposure. Generally middle-aged persons were found to be more susceptible to noise. Higher socioeconomic status and educational level were related to noise annoyance. With regard to sex, findings were less consistent. We also found that results in our studies might be biased due to selective participation, that noise sensitive individuals were likely to have a higher response rate and that inter-study comparison may be difficult since different annoyance scales can produce very different results. In conclusion, the health effects of noise are modified by noise source, co-exposures, environmental and socio-demographic factors (as well as personal traits) and research methodology. To develop better policies for residential noise environment, future research should focus on combined exposures and stressors as well as further explaining age differences and developing better ways to account for social class.