Because of the enormous number of people affected, the impact of air pollution on cardiovascular disease represents a serious public health problem. Results from NIEHS-funded studies have demonstrated a strong relationship between levels of airborne particles, sulfur dioxide, and other fossil fuel emissions and risk of early death from heart disease. The data collected from these landmark studies has prompted federal regulatory agencies to revise existing air quality standards, yielded numerous studies on indoor pollution and respiratory health, and led to the development of air sampling techniques now used in a variety of research settings around the world.
In 1974, NIEHS-funded researchers at Harvard University began a long-term study on residents of six U.S. cities to assess the effects of common air pollutants on respiratory and cardiovascular health. Known as the Six Cities Study, it collected data on more than 8,000 subjects over a period of 14–16 years. The study focused on the health effects of gaseous pollutants such as sulfur dioxide, a colorless gas produced by coal-burning power plants, and fine particle air pollution, microscopic particles that come from motor vehicle exhaust and power plant emissions. The study results showed that subjects living in the more polluted cities had a higher risk of hospitalization and early death from pulmonary and heart diseases as compared to those living in the less polluted cities. The relationship between air pollution and mortality was much stronger for the fine particle component than for the gaseous pollutants.
In a follow-up study sponsored by the NIEHS and the American Cancer Society, researchers measured the cardiovascular effects of fine particle air pollution in a sample of more than 500,000 people in 50 different cities. Once again, there was a strong association between high concentrations of fine particle pollution and increased mortality from cardiopulmonary illness. More recent studies have shown that particles less than 2.5 microns in diameter—about 30 times smaller than the width of a human hair—are more harmful to lung tissue than the larger particles.
Recent data from a four-year study of 11.5 million Medicare enrollees show that small increases in fine particle pollution resulted in increased hospital admissions for heart and vascular disease, heart failure, and chronic obstructive pulmonary disease. Subjects over 75 years of age experienced even greater increases in admissions for heart problems than those younger than 75.
The ultimate goal of NIEHS-sponsored research on air pollution is to provide regulatory agencies with the scientific data that will enable them to develop national air quality standards that adequately protect the health of U.S. citizens. In the meantime, future research must build on these studies to identify those individuals and populations who are most susceptible to the effects of inhaled particles.