Longitudinal relationships between lung cancer mortality rates, smoking, and ambient air quality: a comprehensive review and analysis

Abstract

Lung cancer mortality (LCM) has been associated with smoking and air pollution. This article draws on smoking relationships to clarify air pollution relationships. We analyzed cohort and population-based smoking studies and identified effects of latency and cumulative exposures. We found cogent relationships through longitudinal rather than cross-sectional analysis, thus involving historical data. We also considered passive smoking, occupational exposures, radon, and established carcinogens. We found stable nonsmoking LCM rates during periods of improving ambient air quality. We considered 59 cross-sectional studies of lung cancer and air pollution and found similar statistically significant relative risks for PM2.5, PM10, EC, NO2, SO2, SO2−4, and O3, and minimal risks for benzo(alpha)pyrene and trace metals. Most air pollution studies did not consider latency, exposure duration, or temporal trends; none included estimates of smoking risks implied by their models. We conclude that while LCM studies of smoking, radon, and occupational exposures appropriately considered latency and cumulative exposures; ambient air quality studies have not. Lung cancer has a long memory and exposure histories are required. Effects of cumulative exposures after pollution abatement include substantially reduced risk estimates, delayed health benefits, inability to show accountability for the abatement. However, associations of lung cancer with ambient air pollution cannot be ruled out, especially for historic periods when much higher exposures persisted. Given the major reductions in air quality and smoking habits that have been realized since the Clean Air Act, new studies of LCM and air pollution, including smoking histories and exposure data decades before diagnosis, are needed.HighlightsLifetime cigarette consumption is a good predictor of lung cancer risk.The latent period for lung cancer ranges from about 10 to 30 y.Lung cancer risks for nonsmokers have been stable during the period when ambient air quality improved substantially.Risks of established airborne carcinogens may have been important in the past but not under current conditions.Radon can be important.Air pollution-lung cancer risks should be evaluated jointly with smoking risks but are sensitive to their accuracy.When cumulative exposures to conventional air pollutants are considered rather than concurrent, the applicable risk estimates may decrease by an order of magnitude and abatement benefits will not be readily apparent.Most of the recent cross-sectional studies of lung cancer and regulated air pollutants did not consider latency, duration of exposure, or established carcinogens and their findings have been misinterpreted.Effects of smoking on LCM are now well established as are the spatial distributions of ambient air pollution; however, linkages among the three parameters remain uncertain.