Effects of smoking and antioxidant micronutrients on risk of colorectal cancer.

Background & Aims: Antioxidant intake has been reported to increase the risk of colorectal cancer (CRC) for smokers, yet reduce the risk for nonsmokers. We investigated the association between tobacco smoking and risk of colon or rectal cancer, and whether dietary and supplemental intake of the antioxidant vitamins A, C, E, β-carotene, selenium, zinc, and manganese affects the risk of CRC among smokers.

Methods: Data on smoking habits and antioxidant intake were analyzed for 54,208 participants in the Danish Prospective Diet, Cancer and Health Study. Of these participants, 642 were diagnosed with colon cancer and 348 were diagnosed with rectal cancer. Hazard ratios and 95% confidence intervals were estimated using Cox proportional hazard models. Principal components were used to analyze intake of combinations of antioxidants.

Results: Ever smoking increased the risk for CRC (hazard ratio, 1.19; 95% confidence interval, 1.03-1.37), especially for rectal cancer. Smoking for at least 20 years was associated with a 26% increase in risk of CRC, compared with never smokers, and smoking 20 g tobacco or more each day was associated with a 30% increase in risk. Smoking for more than 30 years, or more than 20 g tobacco each day, was associated with a 48% increase in risk of rectal cancer. We did not observe an interaction between smoking and antioxidant consumption on risk of CRC.

Conclusions: Tobacco smoking increases the risk for CRC. We did not observe that consumption of antioxidant micronutrients modulates the effects of smoking on CRC risk.