Dietary folate intake and lung cancer risk in former smokers: a case-control analysis.

No studies have focused on the role of dietary folate intake in risk of lung cancer in former smokers, in whom dietary folate intake is less likely confounded with current smoking. Therefore, we evaluated the association between dietary folate intake and risk of lung cancer in a population of 470 histopathologically confirmed incident lung cancer cases from M. D. Anderson Cancer Center and 472 cancer-free controls from enrollees at a community-based multispecialty physician practice, frequency-matched on age (5 years), sex, and ethnicity. Dietary folate intake levels were estimated from a National Cancer Institute standard food frequency questionnaire. Unconditional logistic regression analyses were used to calculate the crude and adjusted ORs and their 95% CIs. Dietary folate intake from natural food was significantly higher among the controls than among the cases (P < 0.001), and folate intake above the control median value was associated with a 40% decreased risk of lung cancer (adjusted OR, 0.60; 95% CI, 0.45-0.79). A significant inverse dose-response relationship between increasing dietary folate and decreasing risk of lung cancer was also evident (adjusted OR, 1.02; 95% CI, 0.71-1.47; OR, 0.67; 95% CI, 0.46-0.99; and OR, 0.53; 95% CI, 0.35-0.80 for the second, third, and fourth quartiles of average folate intake, respectively; P for trend <0.001). A more pronounced inverse association between dietary folate intake and lung cancer risk was observed among subjects who drank alcohol, had smoked relatively more, those who did not take supplemental folate, and those who reported a family history of lung cancer. Our data suggest that there is a possible protective role of dietary folate in lung carcinogenesis, a finding which may have implications in public health and cancer prevention.