Daily vitamin D and calcium supplements, taken alone or in combination, failed to reduce the risk of recurrent colorectal adenomas in middle-aged adults, according to a study published online Oct. 14 in the New England Journal of Medicine.
A great deal of evidence suggests that both vitamin D and calcium have antineoplastic properties, particularly in the colorectum. Researchers performed a multicenter, double-blind, placebo-controlled, randomized clinical trial at 11 academic medical centers to test the hypothesis that both agents individually would prevent recurrences in middle-aged patients who had just undergone removal of one or more colorectal adenomas, and that both agents taken together would be more chemoprotective than either one alone.
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The investigators enrolled 2,259 individuals aged 45-75 years who were in good general health and who were expected to undergo follow-up colonoscopy either 3 or 5 years after they had the initial adenoma(s) removed. A total of 419 were randomly assigned to receive calcium alone (1,200 mg daily), 420 to receive vitamin D alone (1,000 IU daily), 421 to receive both supplements, 415 to receive two placebos, 295 to receive calcium plus placebo, and 289 to receive calcium plus vitamin D. Adherence to study medications and to follow-up colonoscopy was excellent, said Dr. John A. Baron of the Geisel School of Medicine at Dartmouth, Hanover N.H., and his associates.
A total of 880 participants were found to have recurrent adenomas during follow-up. Contrary to the investigators’ expectations, the study interventions, both alone and in combination, failed to exert any significant effect on the risk of recurrence. They also failed to affect the risk for advanced adenomas and for distal vs proximal adenomas, the investigators noted (N Engl J Med. 2015 Oct. 15. doi: 10.1056/NEJMoa1500409).
In subgroup analyses, the study interventions also failed to exert any meaningful effect according to patients’ baseline levels of vitamin D or calcium, or according to changes in patients’ vitamin D or calcium intake during the study period.
This study was large enough to detect modest chemopreventive effects. However, the dose of vitamin D was lower than that currently recommended by many experts, and was used for a limited time. So it is possible that vitamin D may have a modest chemopreventive potential, but not one as marked as some have proposed, Dr. Baron and his associates said.