Calcium is the most abundant mineral in the body, and is critical for vascular, muscular, and nervous function, cell signaling, and hormonal secretion.1 The recommendations for calcium intake vary according to age, sex, and for women, during pregnancy or lactation.

Epidemiologic studies suggested a relationship between calcium and colorectal and prostate cancers, which will be the topic of this fact sheet. Some studies are confounded by the combination of calcium and vitamin D supplementation, as calcium improves vitamin D3 absorption, and are excluded from this fact sheet unless a calcium-only group was included.

Colorectal Cancer

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Adenoma Recurrence

A multicenter, double-blind trial randomly assigned 930 patients with colorectal adenoma to receive calcium carbonate (3 g, or 1200 mg elemental calcium) or placebo daily until endoscopic follow-up at 1- or 3-years.2

There was a significant decrease in new adenomas detected at follow-up among patients who received calcium supplementation compared with placebo (adjusted risk ratio [RR], 0.85; 95% CI, 0.74-0.98; P = .03).

Another analysis of this cohort demonstrated that this benefit was particularly evident with advanced preneoplastic polyps, including hyperplastic polyps, tubular adenomas, and histologically advanced neoplasms.3 A long-term follow-up study of this cohort also demonstrated that the protective effect of calcium was maintained up to 5 years after supplementation discontinuation (adjusted RR, 0.63; 95% CI, 0.46-0.87; P = .005).4

Several other trials, however, were not able to replicate these findings.

A multicenter trial randomly assigned 665 patients with colorectal adenoma to receive calcium gluconolactate and carbonate (2 g elemental calcium), fiber (3.5 g ispaghula husk), or placebo daily for 3 years.5 There was no significant difference in adenoma recurrence with calcium supplementation compared with placebo (adjusted odds ratio [OR], 0.66; 95% CI, 0.38-1.17; P = 0.16).

Another multicenter, double-blind trial randomly assigned 2259 patients aged 45 to 75 with a recent colorectal adenoma to receive vitamin D3 (1000 IU), calcium (as carbonate; 1200 mg), both, or neither daily until a 3- or 5-year colonoscopic follow-up.6 There was no significant difference in the number of new adenomas detected at colonoscopic follow-up between the groups, suggesting that calcium supplementation did not prevent colorectal adenoma.

A potential reason for differences in association of calcium supplementation and adenoma recurrence is the baseline calcium:magnesium intake ratio.7 One study found that calcium supplementation had no effect on risk of adenoma recurrence among subjects whose baseline intake ratio was above the median (RR, 0.98; 95% CI, 0.52-0.90), whereas subjects with a low intake ratio demonstrated a significantly lower risk compared with placebo (RR, 0.68; 95% CI, 0.52-0.90).

Colorectal Cancer Recurrence

A randomized pilot study of 220 patients with resected colorectal cancer demonstrated a significant decrease in odds of recurrence with calcium carbonate supplementation compared with placebo (OR, 0.473; 95% CI, 0.266-0.84; P = .011).8