Health effects of combined exposure to surrounding green, air pollution and traffic noise

In daily life, humans are exposed to several environmental factors that can affect human health, such as surrounding green, air pollution and traffic noise. These environmental exposures are spatially correlated due to common sources of air pollution and traffic noise and to absence of these sources in green areas. However, the large majority of studies have evaluated effects of only one of these environmental exposures. Effects of combined exposure to surrounding green, air pollution and traffic noise with cardio-metabolic diseases, poor mental and general health and mortality have been evaluated with survey data from the national Public Health Monitor 2012 (PHM), including almost 400,000 adults. Analyses without correction for the other environmental exposures showed that surrounding green was significantly associated with a lower odds of diabetes, psychological distress, prescribed anxiolytics and poor general health, among others. Air pollution, and to a limited extent traffic noise, were associated with increased odds of these outcomes. In general, in models with correction for the other environmental exposures, associations of surrounding green and air pollution with most health outcomes were attenuated but remained significant, associations of traffic noise disappeared. The combined effects of exposure to surrounding green and air pollution were mostly larger than individual effects of exposures in models without correction for the other exposures. Studies including only one of these three correlated exposures may overestimate the influence on health outcomes attributed to the studied exposure, while underestimating the influence of combined exposures to surrounding green, air pollution and traffic noise.