Calcium: magnesium intake ratio and colorectal carcinogenesis, results from the prostate, lung, colorectal, and ovarian cancer screening trial.

BACKGROUND We aimed to evaluate the associations between calcium and various stages of colorectal carcinogenesis and whether these associations are modified by the calcium to magnesium (Ca:Mg) ratio. METHODS We tested our hypotheses in the prostate lung, colorectal and ovarian cancer screening trial. RESULTS Calcium intake did not show a dose-response association with incident adenoma of any size/stage (P-trend = 0.17), but followed an inverse trend when restricted to synchronous/advanced adenoma cases (P-trend = 0.05). This inverse trend was mainly in participants with Ca:Mg ratios between 1.7 and 2.5 (P-trend = 0.05). No significant associations were observed for metachronous adenoma. Calcium intake was inversely associated with CRC (P-trend = 0.03); the association was primarily present for distal CRC (P-trend = 0.01). The inverse association between calcium and distal CRC was further modified by the Ca:Mg ratio (P-interaction < 0.01); significant dose-response associations were found only in participants with a Ca:Mg ratio between 1.7 and 2.5 (P-trend = 0.04). No associations for calcium were found in the Ca:Mg ratio above 2.5 or below 1.7. CONCLUSION Higher calcium intake may be related to reduced risks of incident advanced and/or synchronous adenoma and incident distal CRC among subjects with Ca:Mg intake ratios between 1.7 and 2.5.