New research denounces the popular notion that vitamin D and calcium can be used to prevent colon cancer. Both nutrients offer many health benefits but unfortunately, preventing colon cancer is not one of them.
Over the last several years, small, randomized trials have been published, each claiming that increasing the amounts of calcium and vitamin D in a diet significantly lowers recurrent colorectal polyp risk. However, the protective role of these nutrients was proven false in a paper published in the New England Journal of Medicine by researchers from the University of North Carolina, Chapel Hill.
The lead researcher of the new study, John Baron MD, was doubly surprised with the results has he had been the author of one of the smaller randomized studies that argued in favor of vitamin D and calcium for preventing polyp recurrence.
“We were especially surprised by the calcium data,” said Baron. “We plan to look at this trial and our previous trial to see if we can explain the difference in findings.”
The new study followed 2,259 people aged 45-75 who had had at least one colorectal adenoma removed within the past 120 days and had no evidence of polyps on follow-up colonoscopy.
The participants were divided into four groups, each with different dietary regimens. The first were to take 1,000 IU of vitamin D3; the second 1,200 mg of calcium as carbonate; the third were instructed to take both doses; and the last group were given a placebo regimen.
After several years (3-5 depending on the case) a follow-up colonoscopy was performed. About 43 percent of the participants had one or more adenomas identified during follow-up colonoscopy. However, in no way did the prescribed regimen dictate who was more likely to have a new tumor.
“We can say with some confidence that at this (1,000 IU) dose, which is a very commonly used dose now, vitamin D does not affect colorectal carcinogenesis,” said Baron. “The calcium story is somewhat more complicated given the strength of the previous evidence.”
The research team can not tell for sure if the result would be different had participants been given larger doses of vitamin D or calcium or if the study had run for a longer time period.
“We started designing this trial around 15 years ago, and at the time there was some concern about toxicity at the dose we used,” he said. “Today 1,000 IU is considered a relatively moderate dose of vitamin D.”
The study was very well designed and had a high adherence rate among participants, despite the large number of people involved in the study.
“This (latest trial) was a large, well-conducted, randomized, placebo-controlled study carried out by experienced researchers that was specifically designed to test whether calcium or vitamin D supplements can prevent colorectal adenomas.”