Synergistic Effects of Air Pollution and Personal Smoking on Adult Pulmonary Function

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Abstract
There is strong evidence that air pollution and cigarette smoking adversely affect respiratory health, but it remains uncertain whether the joint effects of air pollution and smoking are additive or synergistic. The authors investigated the hypothesized synergistic effects of air pollution and personal smoking on pulmonary function in a random sample of 3 287 adults (40–69 y of age) who resided in residential, industrial, and suburban areas in Beijing. The authors used multiple linear regression and adjusted for age, sex, height, education, indoor use of coal stoves, crowding within a house, occupational exposures, and passive smoking. The annual mean total suspended particulates for the period 1981–1985 in residential, industrial, and suburban areas were 389 μg/m3, 449 μg/m3, and 261 μg/m3, respectively, and the annual mean sulfur dioxide levels were 128 μg/m3, 57 μg/m3, and 18 μg/m3, respectively. Compared with individuals in the suburban area, never smokers who resided in the industrial area had a 26-ml (standard error = 39) reduction in forced expiratory volume in 1 s and a 150-ml (standard error = 42) reduction in forced vital capacity; however, smokers in the same area suffered an additional 53-ml (standard error = 38) reduction in forced expiratory volume in 1 s and a 65-ml (standard error = 41) reduction in forced vital capacity. Similarly, never-smokers who resided in the residential area had a 72-ml (standard error = 35) reduction in forced expiratory volume in 1 s and a 274-ml (standard error = 38) reduction in forced vital capacity, and smokers in the same area suffered an additional 75-ml (standard error = 39) reduction in forced expiratory volume in 1 s and a 107-ml (standard error = 42) reduction in forced vital capacity. Long-term exposure to high levels of particulate and sulfur dioxide in Beijing was associated with significantly reduced pulmonary function in both never smokers and smokers. However, the associations were significantly greater among smokers than among never smokers, indicating a synergistic effect of air pollution and personal smoking on adult pulmonary function.