BOSTON—Elderly patients may be more susceptible to the adverse consequences of particulate air pollution if they also have diabetes. In a recent study of the effects of small particulate exposure on hospitalization rates in the elderly, the increased risk of admission for cardiovascular disease (CVD) was more than twice as great among those with coexisting diabetes than it was among other patients.

“The result was the same in both of the age-groups studied,” lead investigator Antonella Zanobetti, PhD, told RESPIRATORY REVIEWS. Patients between ages 65 and 75 years faced the same increase in risk as did those older than 75 years. In contrast, the study found only weak evidence that diabetes raises the risk of hospital admission for respiratory illnesses, such as chronic obstructive pulmonary disease (COPD) and pneumonia. The effect was smaller than it was for CVD and inconsistent by age, said Dr. Zanobetti, a researcher in the Department of Environmental Health at the Harvard School of Public Health in Boston.

WHY DIABETES?

The study focused on diabetes because the disease produces the same cardiovascular disturbances as does airborne particle exposure; among these disturbances are heart rate variability, higher peripheral white cell counts, and increased levels of C-reactive protein and fibrinogen. The investigators therefore hypothesized that patients with diabetes may be at increased risk of cardiovascular events when they are exposed to particulate matter with an aerodynamic diameter less than 10 µm (PM10).

Using Medicare discharge data, Dr. Zanobetti and her coauthor, Joel Schwartz, PhD, examined hospitalization rates for CVD, pneumonia, and COPD in Cook County, Illinois, from 1988 to 1994. The investigators selected Cook County because it is the most populated US county with daily PM10 monitoring. They calculated daily PM10 levels as an average of the values from 10 monitors throughout the county. Two of these monitors measured PM10 almost every day; the others did so less frequently. The mean PM10 during the study period was 33 µg/m3.

The investigators’ statistical analysis of the association between PM10 levels and hospitalization counts took changes in the weather into consideration. Covariates included current and prior day’s temperature, relative humidity, barometric pressure, and day of week.

INCREASE IN RISK

For every 10-µg/m3 increase in PM10 levels, hospital admissions for CVD rose by 2.01% among patients who had diabetes and by 0.94% among those who did not. In patients between ages 65 and 75 years, the rise in CVD admissions associated with increased PM10 levels was 1.89% among those with diabetes and 0.69% among those without. In the older patients, it was 2.03% and 1.25%, respectively.

PM10 levels also markedly increased the risk of hospitalization for respiratory illnesses, but the effect was much less dependent on the presence of diabetes. For every 10-µg/m3 increase in PM10 levels, hospital admissions for pneumonia rose by 2.77% among patients who had diabetes and by 2.20% among those who did not. The comparable increases in COPD admission rates were 2.29% and 1.50%, respectively.

Diabetes appeared to have more of an impact on hospitalization rates for respiratory illnesses when results were stratified by age. It increased the risk of hospitalization for pneumonia in patients between ages 65 and 75 years and for COPD in the older patients.

The investigators acknowledge that their findings do not prove the existence of a synergistic effect between diabetes and particulate air pollution but do strengthen the case for such an effect. “The main point of our study is that people with diabetes are a susceptible population, and more studies on the interaction between diabetes and air pollution are needed,” Dr. Zanobetti stressed. This association could have important public health implications because diabetes is so prevalent: 5% of Americans have diagnosed diabetes and another 3% may have undiagnosed disease.

—Timothy Begany

Reference
1. Zanobetti A, Schwartz J. Are diabetics more susceptible to the health effects of airborne particles? Am J Respir Crit Care Med. 2001;164: 831-833.