A US study has found significant links between the exposure to small particle air pollution and risk of fatal and non fatal heart disease and strokes in older women.
The study is published in the New England Journal of Medicine.
The researchers were based at the University of Washington and used data from the Women’s Health Initiative (WHI) observational study.
Previous studies have assessed deaths due to fine particulate air pollution and compared impact of exposure between cities. But this is the first study to examine links between long term exposure to particles smaller than 2.5 micrometers and cardiovascular events.
Previous research has shown that fine particles in air pollution is linked to pulmonary and coronary heart disease, and also that women are different to men, for instance they have smaller blood vessels, and therefore may be more susceptible to fine particles which get deep into the lungs and cause inflammation that leads to heart disease and strokes.
The scientists examined data from 1994 to 1998 on 65,893 postmenopausal women aged between 50 and 79 who had no record of cardiovascular disease. The women came from 36 different metropolitan areas of the US.
The air pollution was measured by taking readings from meters situated near each woman’s home. These recorded the air pollution level of particles smaller than 2.5 micrometers in aerodynamic diameter (denoted as PM2.5).
After a median period of 6 years, the researchers looked at the women’s medical records again to see what kind and number of first incidence cardiovascular events had taken place during that time.
The scientists then estimated the risk for cardiovascular events against step increases in air pollution measures in the group. They adjusted the figures to take into account demographic, lifestyle, health, education, socio-economic factors. The health factors included smoking status, presence of diabetes, high blood pressure, high cholesterol, and body mass index (BMI).
The results showed that 1,816 of the women (nearly 3 per cent) had either died from or survived cardiovascular events during the follow up period. The events included coronary heart disease, cerebrovascular disease (damage to blood vessels in the brain), heart attack, coronary revascularization (procedures to restore heart function), and stroke.
The exposure concentrations of particles below 2.5 micrometer diameter (PM2.5) ranged from 3.4 to 28.3 micrograms per cubic meter, with a mean level of 13.5. This was measured in the year 2000, toward the beginning of the follow up period.
The limit set last autumn by the Environmental Protection Agency was 15 micrograms per cubic meter. Nearly two thirds of the women in this study were exposed to concentration levels above that limit.
Using these results the researchers showed that each 10 microgram per cubic meter step up in air pollution was linked to a 24 per cent increase in the risk of a cardiovascular event, and a 76 per cent increase in the risk of death from cardiovascular disease.
This is a significantly higher risk than found in previous studies. For instance research by the American Cancer Society puts the increased risk of death from cardiovascular disease for the same step up in PM2.5 at 12 per cent, with 18 per cent increased death risk from ischemic heart disease and 13 per cent from arrhythmia, heart failure, or cardiac arrest, according to an editorial in the same issue of the journal.
The researchers also found that the between city effect was smaller than the within city effect for cardiovascular events.
For cerebrovascular events the risks also increased with steps up in small particle pollution levels (35 per cent increase for each 10 microgram increase in PM2.5).
The first Clean Air Act in the US came into force in the 1960s, and about every ten years since, the standards for air pollution have strengthened. In 1999, the Environmental Protection Agency changed the measuring system from Pollution Standards Index (PSI) to the Air Quality Index (AQI) to take into account the small particle PM2.5 measure, and another one for ozone.
In an accompanying editorial, calls are made to tighten up the regulations even further, for instance to reduce the ceiling on the long term air pollution limits for the PM2.5 particles even further, since this study clearly shows that there is a damaging long term effect to public health.
“Long-Term Exposure to Air Pollution and Incidence of Cardiovascular Events in Women.”
Kristin A. Miller, M.S., David S. Siscovick, M.D., M.P.H., Lianne Sheppard, Ph.D., Kristen Shepherd, M.S., Jeffrey H. Sullivan, M.D., M.H.S., Garnet L. Anderson, Ph.D., and Joel D. Kaufman, M.D., M.P.H.
NEJM Volume 356:447-458, Number 5, February 1, 2007
Website: Original Article