Calcium and Vitamin D and Risk of Colorectal Cancer: Results From a Large Population-based Case-control Study in Newfoundland and Labrador and Ontario

Two-province population-based case-control study in Ontario and Newfoundland and Labrador. CRC cases aged 20-74 years with newly diagnosed colorectal cancer; controls matched by sex and five-year age strata. Final analytic samples: ON: 1,272 cases and 1,830 controls; NL: 488 cases and 651 controls. Dietary intake and supplement use assessed with self-administered questionnaires; province-stratified multivariate unconditional logistic regression adjusting for multiple confounders.

Calcium-containing supplements; Vitamin D-containing supplements; dosage and duration not reported.

In both provinces, controls had higher intake of total calcium and total vitamin D than cases. In Ontario, high intakes of total calcium, total vitamin D, dietary calcium, dietary vitamin D, total dairy products, and milk were associated with reduced CRC risk (e.g., total calcium OR 0.57; total vitamin D OR 0.73; dietary calcium OR 0.76; dietary vitamin D OR 0.77; total dairy/milk OR 0.78). Calcium-containing supplements were linked to ~24-33% risk reduction. In Newfoundland and Labrador, inverse associations were strongest among calcium- or vitamin D-containing supplement users (OR ~0.67–0.68). Conclusion: Total calcium, dietary calcium, total vitamin D, dietary vitamin D, and supplement use may reduce colorectal cancer risk; dairy effects likely reflect calcium and vitamin D, with a suggested joint action of calcium and vitamin D.

Case-control design susceptible to recall and selection biases; potential differential recall; imperfect age matching; measurement error from FFQ; possible nutrient collinearity; lack of sun exposure data; short referent dietary window (1-2 years) may not capture long-term exposures.