Does diet modify the association between lung cancer and ambient particulate air pollution

Background: Particulate air pollution (PM2.5) has been linked to an increase in lung cancer (LC) incidence; however, there is limited knowledge about diet that may modify this association. Objectives: To assess possible effect modification of dietary pattern on the association between ambient PM2.5 and incident LC in single and two-pollutant models with ozone (O3) using the Adventist Health and Smog Study-2 (AHSMOG-2). Methods: At enrollment, the Adventist Health Study-2 (AHS-2), the parent cohort of the AHSMOG-2, obtained dietary information using a food frequency questionnaire and categorized subjects into 2 dietary patterns -vegetarian or non-vegetarian. A total of 80,285 AHSMOG-2 subjects were followed for an average of 7.7 years with respect to LC incidence identified through linkage with U.S. state cancer registries. Ambient air pollution levels at subjects' residence was estimated for the years 2000 and 2001, immediately prior to study start. Possible effect modification, by diet pattern, of the association between ambient PM2.5 and incident lung cancer was assessed. Results: A total of 250 incident LC cases occurred during follow-up. There was a significant interaction between dietary pattern and PM2.5 (p=0.045). Among vegetarian subjects, there was no association between each 10 unit increase in PM2.5 and incident LC (HR=0.70, 95% CI 0.30, 1.60). However, among non-vegetarians, a strong relationship was found (HR=1.91, 95% CI 1.21, 3.03). Conclusion: Our findings suggest that a vegetarian diet attenuates the positive association between ambient PM2.5 and incident LC whereas a non-vegetarian diet seems to increase the risk. Further studies are needed to confirm our findings.