Background: Some epidemiological studies have suggested that high dietary intake of calcium and fibre reduces colorectal carcinogenesis. Available data are not sufficient to serve as a basis for firm dietary advice. We undertook a multicentre randomised trial to test the effect of diet supplementation with calcium and fibre on adenoma recurrence.
Methods: We randomly assigned 665 patients with a history of colorectal adenomas to three treatment groups, in a parallel design: calcium gluconolactate and carbonate (2 g elemental calcium daily), fibre (3.5 g ispaghula husk), or placebo. Participants had colonoscopy after 3 years of follow-up. The primary endpoint was adenoma recurrence. Analyses were by intention to treat.
Findings: 23 patients died, 15 were lost to follow-up, 45 refused repeat colonoscopy, and five developed severe contraindications to colonoscopy. Among the 552 participants who completed the follow-up examination, 94 stopped treatment early. At least one adenoma developed in 28 (15.9%) of 176 patients in the calcium group, 58 (29.3%) of 198 in the fibre group, and 36 (20.2%) of 178 in the placebo group. The adjusted odds ratio for recurrence was 0.66 (95% CI 0.38-1.17; p=0.16) for calcium treatment and 1.67 (1.01-2.76, p=0.042) for the fibre treatment. The odds ratio associated with the fibre treatment was significantly higher in participants with baseline dietary calcium intake above the median than in those with intake below the median (interaction test, p=0.028)
Interpretation: Supplementation with fibre as ispaghula husk may have adverse effects on colorectal adenoma recurrence, especially in patients with high dietary calcium intake. Calcium supplementation was associated with a modest but not significant reduction in the risk of adenoma recurrence.