Calcium does not protect against colorectal neoplasia

Calcium could decrease risk of colorectal neoplasia by binding bowel irritating compounds and diminishing mucosal proliferation. This study quantitatively summarizes epidemiologic studies addressing this hypothesis and aims to explain heterogeneity between studies. Twenty-four articles reported 43 measures of relative risks (RRs). The weighted mean, according to a random effects model, did not indicate substantial protection by calcium [RR = 0.89; 95% confidence interval (CI) = 0.79-1.01]. Results from different studies showed substantial heterogeneity, with the ''true'' underlying RRs ranging from about 0.50 to 1.60. Summary RRs for cohort and case-control studies were 0.90 and 0.88, respectively. For adenomas and carcinomas, RRs were 1.13 (95% CI = 0.91-1.39) and 0.86 (95% CI = 0.74-0.98), respectively, both falling within the range of between study heterogeneity. With respect to subsites, lower RRs were observed for estimates that included proximal colon as one of the subsites (RR = 0.67), whereas the RR was close to 1.0 for distal (RR = 0.97) and rectal subsites (RR = 0.99). Stratification on study characteristics and weighted regression analysis yielded RRs slightly below 1.0, with considerable heterogeneity. These results do not support the hypothesis that calcium prevents colorectal neoplasia.