Short-Term Studies Underestimate Premature Deaths
The APHEA-2 project was a major study of the health effects of air pollution in 30 cities across Europe and in adjacent countries. That and many other studies have reported that short-term changes in PM10 lead to short-term fluctuations in sickness and death. The APHEA-2 project was a major study of the health effects of air pollution in 30 cities across Europe and in adjacent countries. That and many other studies have reported that short-term changes in PM10 lead to short-term fluctuations in sickness and death. This study uses a statistical model– known as the distributed lag model — to explore whether those deaths are advanced by just a few days or a few weeks, or more.
The researchers found that the adverse effects of short-term increases in air pollution persist for more than a month after exposure. The effect size estimate for PM10 doubles for cardiovascular deaths when looking at effects 40 days after exposure, and increases five-fold for respiratory deaths. These results are consistent with higher risk estimates found in cohort studies such as the Harvard Six Cities Study, and strongly suggest that estimates of the effects of short-term exposures to air pollution seriously underestimate the impact of particle exposure.
Researchers conclude that “risk assessment based on the short-term associations likely underestimate the number of early deaths that are advanced by a significant amount, and that estimates based on the cohort studies, or studies such as this one, would more accurately assess the public health impact.”
Another research group took a different approach to evaluate the extent of life-shortening implied by short-term estimates of particulate air pollution on mortality. They sought to establish a separate relative rate of mortality for different time scales. They applied this method of a database on particulate air pollution, daily mortality, and weather in four cities: Pittsburgh, Minneapolis, Seattle, and Chicago.
The authors found larger relative rates of mortality at longer timescales ranging from 14 days to two months, than at short timescales of 1 to 4 days. This refutes the “harvesting hypothesis” that the association between particle concentrations and premature death is entirely due to mortality among very frail persons who lose a few days of life.
Zanobetti, A., Schwartz, J., Samoli, E., Gryparis, A., Tuoloumi, G., Peacock, J., Anderson, R.H., Le Tertre, A., Bobros, J., Celko, M., Goren, A., Forsberg B., Michelozzi, P., Rabczenko, D., Perez Hoyos, S., Wichmann, H.E., and Katsouyanni, K. The Temporal Pattern of Respiratory and Heart Disease Mortality in Response to Air Pollution. Environmental Health Perspectives. Vol. 111, No. 9, pp. 1188-1193, July 2003.
The National Institute of Environmental Health Sciences [http://ehis.niehs.nih.gov/] makes the full article available for free online.
Dominici, F., McDermott, A., Zeger, S.L., and Samet, J.M. Airborne Particulate Matter and Mortality: Timescale Effects in Four US Cities. American Journal of Epidemiology. Vol. 157, No. 12, pp. 1055-1065, June 15, 2003.
The National Library of Medicine [www.ncbi.nlm.nih.gov/entrez/] offers the abstract online.
