Colorectal cancer risk and dietary intake of calcium, vitamin D, and dairy products: A meta-analysis of 26,335 cases from 60 observational studies

In vivo and in vitro studies suggest that dairy products, calcium, and dietary vitamin D inhibits the development of colorectal cancer (CRC). A meta-analysis was performed to evaluate this relationship in observational studies. Data from 60 epidemiological studies enrolling 26,335 CRC cases were pooled using a general variance-based meta-analytic method. Summary relative risk (RR) estimates and 95% confidence intervals (CIs) were calculated for the highest vs. the lowest intake categories. Sensitivity analyses tested the robustness of these summary effect measures and the statistical heterogeneity. The summary RR for high milk and dairy product intake, respectively, on colon cancer risk was 0.78 (95% CI = 0.67-0.92) and 0.84 (95% CI = 0.75-0.95). Milk intake was unrelated to rectal cancer risk. High calcium intake had a greater protective effect against tumors of the distal colon and rectal cancer vs. proximal colon. The risk reduction associated with calcium was similar for dietary and supplemental sources. Vitamin D was associated with a nonsignificant 6% reduction in CRC risk. Higher consumption of milk/dairy products reduces the risk of colon cancer, and high calcium intake reduces the risk of CRC. Low vitamin D intake in the study populations may limit the ability to detect a protective effect if one exists.