Plain language summary
Calcium and vitamin D may play a role in colorectal cancer incidence. One possible explanation is that they may act synergistically on a number of mechanisms to protect against recurrence of colonic adenomas. The aim of the study was to determine the effects of a high-fibre, high-fruit and vegetable, and low-fat diet on the recurrence of adenomatous polyps in the large bowel. For the present study, 1905 participants from the 2079 Polyp Prevention Trial participants who completed the full trial follow-up were evaluated. The participants’ diet was assessed at baseline and annually, and they also received full colonoscopies at baseline, their 1-year visit and at the end of the trial i.e. 4 years after randomization. Results show that there were no significant associations between any of the adenoma recurrence outcome variables and dietary or total calcium intake, consumption of low or high-fat dairy products or dietary vitamin D intake. However, total vitamin D intake was weakly inversely associated with adenoma recurrence. Calcium and vitamin D supplementation were also inversely associated with single and multiple adenoma recurrence. The study shows that calcium and vitamin D intake may provide weakly protective associations with the risk for recurrence of adenoma polyps.
Abstract
The Polyp Prevention Trial (PPT) was a multicenter randomized clinical trial designed to determine the effects of a high-fiber, high-fruit and vegetable, low-fat diet on the recurrence of adenomatous polyps in the large bowel. Detailed dietary intake and supplement use data were collected at baseline and at each of 4 annual study visits. Adenoma recurrence was ascertained by complete colonoscopy at baseline and after 1 and 4 y. Recurrence was found in 754 of the 1905 trial participants. We evaluated the association between calcium and vitamin D intake and adenomatous polyp recurrence after adjusting for intervention group, age, gender, nonsteroidal anti-inflammatory drug use, total energy intake, and the interaction of gender and intervention group. Vitamin D models were also adjusted for the location of the clinic site. Dietary variables were adjusted for total energy intake via the residual method. There were no overall significant associations between adenoma recurrence and dietary calcium intake [odds ratio (OR) for the 5th compared with the lowest quintile = 0.91; 95% CI = 0.67-1.23; P-trend = 0.68], total calcium intake (OR = 0.86; 95% CI = 0.62-1.18; P-trend = 0.20), or dietary vitamin D intake (OR = 0.93; 95% CI = 0.69-1.25; P-trend = 0.43) averaged over follow-up. Total vitamin D intake was weakly inversely associated with adenoma recurrence (OR = 0.84; 95% CI = 0.62-1.13; P-trend = 0.03). Supplemental calcium and vitamin D use during follow-up also were inversely associated with adenoma recurrence (OR for any compared with no use = 0.82; 95% CI = 0.68-0.99; and OR = 0.82; 95% CI = 0.68-0.99; for calcium and vitamin D, respectively). Slightly stronger associations were noted for the prevention of multiple recurrences. Our analyses did not suggest a significant effect modification between total calcium and total vitamin D intake (P = 0.14) on risk for adenoma recurrence. This trial cohort provides some evidence that calcium and vitamin D may be inversely associated with adenoma recurrence.
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