The objective of the study is to estimate the differences in the impact of diet and physical exercise on lung cancer risk in female nonsmokers vs. smokers, and reveal interactions, if any. In a hospital based case-control study, data collected by in-person interviews from 569 female lung cancer cases and 2120 controls were analyzed using unconditional logistic regression stratifying by appropriate factors. Protective effects were observed for intake of milk/dairy products (OR=0.57, 95%CI 0.35-0.94), vegetables (OR=0.60, 95%CI 0.40-0.91), apples (OR=0.69), wine (OR=0.77), and physical exercise (OR=0.59, 95%CI 0.42-0.83) among smokers only, while no similar effects were found among nonsmokers. In contrast, the intake of black tea was associated with a protective effect (OR=0.66, 95%CI 0.47-0.94) among nonsmokers only. Comparing the effects of dietary items and physical activity on lung cancer risk among nonsmokers versus smokers, statistically significant effect modifications were found for black tea (P 0.005), and milk/dairy products (P 0.047). Borderline effect modifications emerged for physical exercise (P 0.077).
Conclusions: These results indicate protective effects of some components of healthful diet and physical exercise among smokers, and of the intake of black tea among nonsmokers. The observed interactions of the impact of black tea, milk/dairy products and physical activity upon lung cancer risk in women at different levels of the smoking habit deserve further studies.