The indirect effect of fine particulate matter on health through individuals’ life-style

Limited literature has been published on the association between environmental health indicators, life-style habits and ambient air pollution. We have examined the association of asthma prevalence and the amount of health investment with daily mean concentrations of particulate matter (PM) with a mass median aerodynamic diameter less than 2.5mm (PM2.5) in 16 metropolitan areas in U.S. using the Behavioral Risk Factor Surveillance System (2001) data in conjunction with the Air Quality System data collected by the Environmental Protection Agency. A multivariate probit approach has been used to estimate recursive systems of equations for environmental health outcome and life-styles. A piecewise linear relationship has been postulated to describe the association between health outcome, health investment and pollution. We have assumed one change point at AQI value of 100 which corresponds to the US national air quality standard. The most interesting result concerns the influence of pollution on health-improving life-style choices: below a specified threshold concentration (AQI=100) a positive linear association exists between exposure to PM2.5 and health investments; above the threshold the association becomes negative. Hence, only if ambient pollution is in the ‘satisfactory range’ (AQI level at or below 100), individuals will have incentive to invest in health.