Background: Although substantial evidence suggests that higher intake of fruits and vegetables can reduce the adverse impact of smoking on lung cancer risk, great uncertainty exists regarding the specific foods and their constituents that are protective. We therefore examine prospectively the relation between cigarette smoking and lung cancer incidence among women, and quantify the associations between dietary antioxidants, other nutrients, and lung cancer risk.
Methods: In a 16-year prospective cohort study (the Nurses' Health Study), 593 cases of lung cancer were confirmed during 1,793,327 person-years of follow-up. Dietary data, including vitamin supplement use and food intake, were collected in 1980 using a validated semiquantitative food frequency questionnaire.
Results: The risk of lung cancer increased with the number of cigarettes smoked and with early onset of cigarette smoking. The risk decreased rapidly with the discontinuation of smoking but took 15 years to fall to about the level of risk for women who had never smoked. Dietary intake of fat was not related to the risk of lung cancer. Although beta-carotene intake was not related to risk, intake of carrots showed a strong inverse relation: women who reported consuming five or more carrots per week had a relative risk of 0.4 (95% CI = 0.2-0.8) compared with the risk for women who never ate carrots.
Conclusions: Smoking is the most important risk factor for lung cancer in women, as it is in men. Higher vegetable consumption, particularly of carrots, may significantly reduce the risk of lung cancer, but dietary modification cannot be considered a substitute for smoking prevention and cessation.