Science Selection September 2008 | Volume 116 | Issue 9
The Cool Factor: Season Modifies Cardiorespiratory Deaths in China
Citation: Potera C. 2008. The Cool Factor: Season Modifies Cardiorespiratory Deaths in China. Environ Health Perspect 116:A394; http://dx.doi.org/10.1289/ehp.116-a394b
Published: 1 September 2008
Outdoor air pollution has been linked with increased risk of death from cardiorespiratory disease in epidemiologic studies in North America and Europe. Some studies have found that sex, age, or other modifying factors can cause increased susceptibility to air pollution in some individuals. However, few of these studies have been conducted in Asia. Now a new study of Shanghai residents reveals that the elderly, women, and individuals with lower educational backgrounds are especially vulnerable to outdoor air pollution during cooler weather [EHP 116:1183–1188; Kan et al.].
The researchers examined death certificates recorded between 1 January 2001 and 31 December 2004 in the central area of Shanghai and found an average of 119 nonaccidental deaths reported daily, with 49.1% due to cardiorespiratory disease. They collected daily air pollution data for particulate matter less than 10 μm in diameter (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), and ozone (O3) from the Chinese government agency that tracks air pollutants and assessed how mortality and pollutant levels varied by sex, age, educational status, and season of the year.
They found that most air pollutant levels peaked in the cool season (October through March, when the temperature averages 58°F), correlating with a peak in the death rate; the exception was O3, which had higher concentrations in the warm season (April through September, when the temperature averages 75°F). They observed a 2- to 3-times greater risk of death from cardiorespiratory disease in the cool season compared with the warm season, with SO2, NO2, and O3 particularly showing seasonal differences in association with cause of death. The same air pollutants were also associated with a 3- to 4-fold greater risk of cardiovascular death in the cool season than in the warm season, possibly because exposure to air pollutants is reduced by staying inside air-conditioned buildings.
Additionally, people older than 65 were up to 5 times more likely than younger people to die of cardiorespiratory disease. Compared with men, deaths in women were twice as likely to be linked to elevated O3 and PM10 levels. This may be due to men’s greater rate of smoking, the effects of which may override pollution-related effects in male smokers. Overall, people with less education were twice as likely as more educated residents to die during periods of elevated pollution. Educational level, a reflection of socioeconomic status, has been reported previously as a modifying factor for air pollution–related deaths in North America and Europe, but this is the first such report from mainland China, where the concentrations of PM10, SO2, and NO2 are much higher.