CALCIUM supplements have been shown to increase the risk of developing certain types of precancerous growths in the rectum or colon up to 10 years after administration. Originally thought to prevent colorectal polyps, analysis of data from a randomised clinical trial has indicated that calcium supplements with and without vitamin D correlated with a higher incidence of serrated polyps on colonoscopy.
Polyps are noncancerous growths that can develop into colorectal cancer, a condition that was responsible for the deaths of 27,150 and 23,110 North American males and females, respectively, in 2017. Previously, calcium and vitamin D have been investigated as chemoprevention agents to reduce the incidence of colorectal cancer and its precursors; however, studies on the effect of polyp prevention have produced inconsistent results.
Therefore, researchers from several American research centres analysed data from a recent chemoprevention trial of calcium and vitamin D, which included 2,259 patients aged 45–75 years who had had at least one colorectal adenomatous polyp removed following an initial baseline screening. Patients with no family history of colorectal cancer, inflammatory bowel disease, or other serious conditions were randomly assigned to four daily treatment groups: calcium supplements, vitamin D supplements, both calcium and vitamin D supplements, or no supplements.
All treatment groups were kept in the treatment phase for 3–5 years, until the next screening colonoscopy, after which the supplementation was stopped. After this observation phase, 6–10 years after the start of supplementation, a third screening colonoscopy was performed. Neither vitamin D nor calcium supplementation had an effect on the incidence of serrated polyps after the treatment phase; however, the final colonoscopy revealed a correlation between the prevalence of serrated polyps and calcium supplementation 6–10 years prior, both with and without vitamin D. In addition, women and smokers had the highest risk of developing serrated polyps after taking calcium supplements.
Although these data were from a large randomised clinical trial, the authors noted that additional investigations are required: “Further studies are recommended to confirm these results, which may have important implications for [colorectal cancer] screening and prevention.” Since these results oppose the idea that calcium is a chemoprevention agent, the researchers advised that people who have had precancerous serrated polyps may wish to avoid taking calcium or vitamin D supplements, particularly women and smokers.