Background: A range of plausible biological mechanisms support preventive effects of micronutrients in bladder cancer. So far, however, results from the few epidemiological studies on the relation have been inconsistent, with no clear associations found.
Objective: To evaluate the association between total, dietary, and supplemental intake of beta-carotene, folate, vitamins C and E, and risk of urothelial carcinoma (UC) and to explore whether the association differs with smoking status.
Design, setting, and participants: The association was evaluated in the Danish Diet, Cancer and Health Study, comprising 55,557 men and women aged 50-64 yr at inclusion with no previous cancer diagnosis.
Measurements: At baseline, all participants completed a detailed food frequency questionnaire including information on consumption of vitamin C, E, folate, and beta-carotene from diet and supplements. Incidence rate ratios (IRRs) of UC were calculated using Cox proportional hazards models.
Results and limitations: During a median of 10.6 yr of follow-up, 322 UC cases were diagnosed. Vitamin C, E, and folate showed no association with UC, regardless of source. There was a significantly lower risk of disease with dietary beta-carotene consumption (IRR: 0.82; 95% confidence interval [CI]: 0.69-0.98) and a borderline significant lower risk with total beta-carotene intake (IRR: 0.85; 95% CI: 0.73-1.00) pr. 5000 μg of intake. We found a significant interaction between both dietary (p=0.005) and total (p=0.002) beta-carotene and smoking status, with a significant protective effect of beta-carotene seen among current smokers only.
Conclusions: Our results indicate no preventive effect of vitamin C, E, or folate on UC. We found a protective effect of dietary, but not supplemental, beta-carotene on UC, but further studies are required.