Air pollution and the heart: cardiovascular effects and mechanisms

There has been increasing awareness in recent years of the adverse cardiovascular effects of ambient air pollution. The recent publication of a statement from the Expert Panel on Population and Prevention Science of the American Heart Association has highlighted this issue. It has been appreciated for several decades that major pollution episodes, such as that associated with the London Fog of 1952, are responsible for increased numbers of deaths and most of these are due to cardiorespiratory causes. Realisation of this prompted government and environmental health initiatives to reduce emissions through establishing air quality standards. Previously, the major sources of air pollution were related to domestic coal burning and industry. However, the pattern of emissions in modern developed countries has changed, resulting in a pollution mixture of different composition to that on which early air quality standards were based. Even current 'lower' levels of air pollution have been shown consistently to be associated with adverse health effects. Over the past two decades, a wealth of epidemiological studies have considered both long- and short-term health effects of air pollution. Although the relative risk of respiratory disease in relation to air pollution exposure seems to be higher than that of cardiovascular disease, the latter are of greater absolute significance in population terms. A number of hypotheses have been proposed in order to explain the observed associations, and recent research efforts have focused on examining the mechanisms underlying the effects. It is suggested that certain subgroups of the population such as the elderly or those with pre-existing cardiorespiratory disease may be more susceptible to the effects of air pollution, and analysis of survival data from cohort studies supports this observation.