Diet and prostate cancer risk in a cohort of smokers, with a specific focus on calcium and phosphorus (Finland)

Background: Calcium, phosphorus, fructose, and animal protein are hypothesized to be associated with prostate cancer risk, potentially via their influence on 1,25-dihydroxyvitamin D-3. We examined these nutrients and overall diet and prostate cancer risk in the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study (ATBC Study). Materials and methods: The ATBC Study was a randomized 2 x 2 trial of alpha-tocopherol and beta-carotene on lung cancer incidence conducted among Finnish male smokers; 27,062 of the men completed a food-use questionnaire at baseline, and comprise the current study population. There were 184 incident clinical (stage 2-4) prostate cancer cases diagnosed between 1985 and 1993. We used Cox proportional hazards models to examine associations between dietary intakes and prostate cancer. Results: We did not observe significant independent associations for calcium and phosphorus and prostate cancer risk. However, men with lower calcium and higher phosphorus intake had a multivariate relative risk of 0.6 (95% CI 0.3-1.0) compared to men with lower intakes of both nutrients, adjusting for age, smoking, body mass index, total energy, education, and supplementation group. Of the other foods and nutrients examined, none was significantly associated with risk. Discussion: This study provides, at best, only weak evidence for the hypothesis that calcium and phosphorus are independently associated with prostate cancer risk, but suggests that there may be an interaction between these nutrients.