BACKGROUND: In urban areas, traffic-related noise and air pollution may be correlated, thus effects mutually confounded. To disentangle effects, considering peoples’ exposure indoors is essential. This has not been done so far which may explain inconsistent findings for blood pressure (BP) and hypertension (HT) and these two environmental stressors. We integrate for the first time indoor traffic noise to disentangle their effects.
AIMS: We analysed associations of long-term exposure to home outdoor nitrogen dioxide (NO2) and outdoor and indoor estimates of traffic noise levels with HT, systolic BP (SBP), and diastolic BP (DBP; mmHg).
METHODS: We evaluated 1926 participants at baseline (years 2003-2006) from the Catalan REGICOR cohort. We collected data on measures against noise at home indoors. Outdoor residential traffic noise at night (Lnight) and NO2 levels were estimated at façades with a city-specific noise model and land-use regression model, respectively. Individual indoor traffic noise levels were derived subtracting from outdoor noise the dB(A) reduction provided by reported noise protections, according to literature. Multivariate linear regression models were adjusted for NO2 and either outdoor or indoor noise.
RESULTS: Median levels of home outdoor NO2 were 26.62µg/m3, of outdoor noise 55.96dB(A) and of indoor noise 46.11dB(A). Spearman correlations between outdoor and indoor noise with NO2 were 0.76 and 0.38, respectively. In the outdoor noise model, NO2 was associated only with BP and noise only with HT. In the indoor noise model, HT and BP showed more plausible patterns for both exposures (per IQR): NO2 (HT: OR=1.18, 95%CI: 0.98,1.42; SBP: ?=1.60, 95%CI: 0.31,2.89; DBP: ?=0.69, 95%CI:-0.9,1.46) and noise (HT: OR=1.06, 95%CI: 0.99,1.14, SBP: ?=0.38, 95%CI: -0.1,0.87).
CONCLUSION: Our preliminary findings indicate that proper estimates of indoor noise exposure from outdoor sources are essential to investigate the independent effects of both traffic-related environmental stressors on HT and BP.
