Noise levels and cardiovascular mortality: a case-crossover analysis

The relationship between occupational noise and cardiovascular outcomes has been widely investigated. Regarding environmental noise levels, the attention is focused on road traffic noise due to the large number of exposed persons and the large periods of exposure. There are few studies assessing the short-term effects of traffic noise on cardiovascular outcomes. The aim of this study was to quantify the short-term effects of urban noise levels on age-specific cardiovascular mortality.

A case-crossover design was used. Daily mortality counts in Madrid city due to cardiovascular causes (ICD codes: 390-459) from 1 January 2003 to 31 December 2005 were obtained. Data noise levels were collected as diurnal equivalent noise (Leqd8-22 h), night equivalent noise (Leqn22-8 h), and daily equivalent noise (Leq24 h). Confounding variables as daily levels of air pollutants, temperature, and relative humidity data were controlled. Overdispersed Poisson regression models were adjusted to control for both seasonality and time trends. Estimated effects are reported as percentage increase in the relative risk (IRR) associated with an increase of 1 dBA.

The strongest associations between all noise exposure levels and cardiovascular mortality were reported at lag 1: IRR 4.5% (95% CI 0.6, 8.7%), IRR 3.9% (95% CI 0.6, 7.3%), and IRR 6.2% (95% CI 2.1, 10.6%) for Leqd, Leqn, and Leq24, respectively. Analysing by age-specific groups at lag 1, statistically significant associations were found for those aged ≥65: 4.5% (95% CI 0.3, 8.9%), 3.4% (95% CI 0.1, 6.9%), and 6.6% (95% CI 2.2, 11.1%) for Leqd, Leqn, and Leq24, with no substantial changes in the effects of noise exposure levels at lag 1 after adjusting for PM2.5 and NO2.

The association found between noise exposure levels and cardiovascular mortality suggests a joint effect of diurnal and night-time noise levels. Our results also reveal independent effects of noise exposure levels and the air pollutants analysed. This strongly suggests the need to seriously consider the high noise exposure levels reported as an important public health issue.