Air pollution and hospitalization due to angina pectoris in Tehran, Iran: A time-series study

Background: Health effects of air pollution have been studied in many different parts of the world. Although a fairly large number of studies have explored the cardiovascular impacts of air pollution, because of its unique location we studied the association between air pollutants and hospital admissions due to angina pectoris in Tehran for the first time. Methods: This is a retrospective time-series study. The variables of the study include the levels of five air pollutants-nitrogen dioxide (NO2), carbon monoxide (CO), ozone (O3), sulfur dioxide (SO2), and particulate matter <10 μm in aerodynamic diameter (PM10)-as independent variables; daily hospitalizations due to angina pectoris in 25 academic hospitals in Tehran as the dependent variable; and mean daily temperature and humidity, seasonality, time trend, and day of the week as potential confounders. All variables were measured during a 5-year period from 21 March 1996 to 20 March 2001. The data of mean daily levels of NO2, CO, O3, SO2, and PM10 were collected from one of the stations of Tehran's Air Quality Control Corp. Data were analyzed using Poisson regression models. Relative risks of angina pectoris admissions were calculated for an increase in 1 mg/m3 for CO and 10 μg/m3 for the other pollutants. Results: Daily admissions due to angina pectoris were significantly related to the CO level, after controlling for confounder effects. Each unit increase in the CO level caused a 1.00934 increase in the number of admissions (95% CI, 1.00359-1.01512). This association was verified with a lag of 1 day. There was no significant association between the other air pollutants and the number of daily admission due to angina pectoris. Conclusions: We found that with increasing levels of the pollutant CO, the number of admissions due to cardiac angina rose. Ischemic heart disease is the leading cause of death in Iran. Air pollution control will reduce the number of this preventable disease and resulting deaths.