Dietary iron, zinc, and calcium and the risk of lung cancer

Background: Iron, zinc, and calcium are all involved in the metabolism of reactive oxygen species and may compete with each other for similar binding sites. Dietary intakes of these micronutrients have been associated with altered risks of colorectal, breast, and prostate cancers. Methods: In this Massachusetts hospital-based case-control study of 923 patients with lung cancer and 1125 healthy controls, we studied the associations between dietary iron, zinc, and calcium intake and the risk of lung cancer. Dietary intake was assessed at the time of recruitment (1992 to 2000) with the use of a 126-item semiquantitative food-frequency questionnaire. We analyzed the data using multiple logistic regression models adjusting for smoking history and other potential risk factors. Results: The adjusted odds ratios of dietary iron, zinc, and calcium from food sources were 1.45 (95% confidence interval = 1.03-2.06), 0.71 (0.50-0.99), and 1.64 (1.17-2.29), respectively, for the highest quintile versus the lowest quintile of each micronutrient. Stronger associations between micronutrients and lung cancer risk were found when iron, zinc, and calcium were included together in the same model. The associations between dietary micronutrients intake and lung cancer risk were stronger among current smokers than among former smokers. When we examined intake from supplements as well as diet, associations were similar to those for diet alone. Conclusions: Dietary iron, zinc, and calcium may play an important role in the development of lung cancer, especially among current smokers. These results need to be confirmed in large prospective studies.