Many studies have suggested a role for calcium in reducing the risk of colorectal adenomas and cancer but its effectiveness may be dependent on interactions with other dietary and/or lifestyle factors. We examined the association between calcium and prevalence of adenomas and assessed whether the association was stronger in biologically plausible subgroups.
Cross-sectional data from 222 cases and 479 adenoma-free controls who underwent colonoscopies and completed food frequency and lifestyle questionnaires were used in the analyses. Multivariable logistic regression was used to estimate the association between calcium and prevalence of adenomas. Stratified analyses and the likelihood ratio test were used to examine effect modification by various demographic, lifestyle, and behavioral factors.
Overall, little association was observed comparing total calcium intake of ≥900 mg/day to <500 mg/day (adjusted odds ratio [OR] = 0.85, 95% confidence interval [CI]: 0.53–1.37). However, stronger associations were observed in patients with lower fat intake and in those who regularly (≥15 times/month) took nonsteroidal antiinflammatory drugs (NSAIDs). Specifically, total calcium intake of ≥900 mg/day was associated with a lower prevalence of adenomas among patients with lower fat intake (OR = 0.47, 95% CI: 0.25–0.91) but not among those with higher fat intake (OR = 1.20, 95% CI: 0.61–2.35; P-value for interaction = .01). For NSAIDs, the associations were OR = 0.37 (95% CI: 0.16–0.86) for regular NSAID users and OR = 1.27 (95% CI: 0.73–2.22) with infrequent or nonuse of NSAIDs, respectively (P = .06).
The data suggest that a lower-fat diet and regular NSAID use may enhance calcium's effectiveness as a colorectal cancer preventive agent. Cancer 2007 © 2007 American Cancer Society.