Does dietary calcium interact with dietary fiber against colorectal cancer? A case–control study in Central Europe

Hospital-based case-control design conducted in Krakow, Poland, 2000–2012. Participants: 703 incident colorectal cancer cases (histologically confirmed colon or rectal adenocarcinomas) and 853 hospital-based controls. Adults aged ≤75. Dietary intake assessed with a 148-item semi-quantitative FFQ; data collected on demographics, lifestyle and diet covariates; analyses used multivariable logistic regression with unadjusted, age/gender/education-adjusted, and fully adjusted models.

Higher dietary calcium intake (>1000 mg/day) is associated with lower risk of colorectal cancer, particularly colon cancer. A 100 mg/day increase in calcium corresponded to a 5% reduction in colorectal cancer risk (OR 0.95; 95% CI 0.92–0.99). Calcium intake >1000 mg/day linked to a 46% lower colon cancer risk (OR 0.54; 95% CI 0.35–0.83) and a ~30–37% lower colorectal cancer risk (OR 0.70; 95% CI 0.51–0.96) overall. The protective effect is modified by dietary fiber (p for interaction 0.003 for colorectal cancer; 0.015 for colon cancer). Stronger protection observed with higher fiber intake; in the highest fiber category (≥6 g/day) and very high calcium (e.g., >2000 mg/day) colon cancer risk OR ~0.23 (95% CI 0.09–0.56). No significant association for rectal cancer. Conclusion: High dietary calcium, especially with high fiber intake, may be linked to lower colon cancer risk; causal inference limited by observational design; further research needed to confirm across higher fiber intakes.

Retrospective case-control design with potential recall and selection biases; hospital-based controls may limit generalizability; possible unmeasured confounders (e.g., NSAID use, vitamin D status); dietary intake assessed by FFQ with inherent measurement error; missing data handled by pairwise deletion.