Calcium supplementation for the prevention of colorectal adenomas: A systematic review and meta-analysis of randomized controlled trials

Table 1 Randomized, double-blind, placebo-controlled trials of calcium supplementation for prevention of colorectal adenomas

Study or subgroup1	Participants randomized	Mean age (yr)	Women	Follow-up (mo)	Amount of elemental calcium supplemented (mg/d)
Vitamin D/Calcium Polyp Prevention Study[27]	1675	59	15%	36 or 60	1200
SWOG Calcium Chemoprevention Pilot Study[47]	220	682	37%	60	1800
ECP Calcium Fibre Polyp Prevention Study[28]	439	59	37%	36	2000
Calcium Polyp Prevention Study[51,52]	930	61	28%	48	1200

¹For the Vitamin D/Calcium Polyp Prevention Study, only a subgroup was taken into account in the analysis;

²Median value. ECP: European Cancer Prevention Organisation; SWOG: Southwest Oncology Group.

Table 2 Summary of findings

	Illustrative comparative risks (95%CI)
	Assumed risk	Corresponding risk
	Placebo	Calcium
Recurrence of adenomas (follow-up: 3 to 5 yr)	462 per 1000	411 per 1000	Relative effect (95%CI): RR = 0.89 (0.82-0.96)
		(379 to 444)	No. of patients with follow-up evaluation: 2984
			No. of RCTs: 4
			Quality of evidence (GRADE): ++++ (high)
Advanced adenomas (follow-up: 3 to 5 yr)	113 per 1000	104 per 1000	Relative effect (95%CI): RR = 0.92 (0.75-1.13)
		(85 to 128)	No. of patients with follow-up evaluation: 2998
			No. of RCTs: 4
			Quality of evidence (GRADE): +++- (moderate)

(1) the basis for calculating the assumed risk is the overall event rate across the trial groups receiving placebo; (2) the corresponding risk (calcium group) is based on the assumed risk and the relative effect estimate (risk ratio); (3) the relative effect estimate and its 95%CI come from a Mantel-Haenszel fixed-effects meta-analytic model; and (4) the overall quality of evidence is judged as “high” for recurrence of adenomas, and “moderate” for advanced adenomas. A high quality of evidence means that “we are very confident that the true effect lies close to that of the estimate of the effect”, while a moderate quality of evidence means that “we are moderately confident in the effect estimate. The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different”[58]. Population: Patients with colorectal adenomas removed before enrollment. Intervention: Calcium supplementation (1200-2000 mg/d) to prevent recurrence of adenomas. Comparison: Placebo. RR: Risk ratio; GRADE; Grading of Recommendations Assessment, Development and Evaluation; RCTs: Randomized controlled trials.