Disentangling the effects of traffic-related noise and air pollution on blood pressure: indoor noise levels and protections

Abstract

Outdoor road traffic noise levels are associated with hypertension (HT). Studies on blood pressure (BP) are inconsistent and the true indoor traffic noise exposure may differ due to protections against noise. We analysed the effects of long-term exposure to outdoor and indoor traffic noise levels on HT, systolic (SBP) and diastolic BP (DBP, mmHg), adjusting for outdoor annual average concentrations of near-road traffic-related air pollution (nitrogen dioxide, NO2) among 1926 participants (aged 36-82) from the Catalan REGICOR study. Long-term outdoor residential levels of traffic noise at night (Lnight, in A-weighted dB) and annual averages of NO2 (in µg/m3 ) were estimated at the postal addresses’ façades with a city-specific noise model and a land-use regression model, respectively. Indoor traffic noise was calculated from outdoor noise levels subtracting the attenuations in dB according to reported noise protections. Median noise levels were 56.7 dB outdoors and 27.1 dB indoors. Spearman correlations between outdoor and indoor noise with NO2 were 0.75 and 0.23, respectively. Outdoor noise was only associated with HT (OR=1.19, 95%CI: 1.02, 1.40), whereas there was a suggestive association of indoor noise with both HT (OR=1.06, 95%CI: 0.99, 1.13) and SBP (ß=0.38, 95%CI: -0.08, 0.83) per 5 dB increase in outdoor noise levels. NO2 was also associated with both outcomes after adjustment for indoor noise. Findings for indoor traffic noise levels are more plausible than those for outdoor traffic noise. The use of indoor traffic noise estimates help to disentangle the effects from those of traffic-related air pollution.