Seasonal variation of effect of air pollution on blood pressure.

BACKGROUND Many studies have shown a consistent association between ambient air pollution and an increase in death due to cardiovascular causes. An increase in blood pressure is a common risk factor for a variety of cardiovascular diseases. However, the association between air pollution and blood pressure has not been evaluated extensively. METHODS In this cross-sectional study, we measured blood pressure in 10,459 subjects who had a health examination from 2001 to 2003, and calculated individual's exposure to ambient levels of air pollutants. To evaluate the relationship between exposure to air pollutants and blood pressure with respect to season, we performed a multiple regression analysis, separately, according to season, controlling for individual characteristics and meteorological variables. RESULTS In the warm-weather season (July-September), particulate air pollutant of <10 microm (PM(10)) and nitrogen dioxide (NO(2)) concentrations were significantly associated with measures of blood pressure. During cold weather (October-December), blood pressure was significantly associated with sulphur dioxide (SO(2)) and ozone (O(3)) concentrations. The significant association between PM(10) or NO(2) and blood pressure disappeared during the cold-weather season. CONCLUSION We found a seasonal variation for the association between ambient air-pollutant concentrations and blood pressure.