Monthly, long-term high-dose vitamin D supplementation without calcium may not be associated with a reduced risk of cancer, according to a study published in JAMA Oncology.

A previous hypothesis stated that low levels of vitamin D may be a risk factor for several types of cancer, but evidence from randomized clinical studies assessing vitamin D supplementation have been conflicting.

For this post-hoc analysis of the Vitamin D Assessment (VIDA) study, researchers assessed the incidence of all primary invasive and in situ malignant neoplasms of 5108 patients randomly assigned to oral vitamin D3 or placebo. Patients received an initial bolus dose of vitamin D3 200,000 IU, then monthly doses of 100,000 IU thereafter for a median of 3.3 years. Deseasonalized mean vitamin D concentration was 26.5 (9.0) ng/mL, and the median age was 65.9 years.

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Overall, there were 328 total cases of cancer; 6.5% (165) and 6.4% (163) of patients in the vitamin D and placebo groups, respectively, reported a primary outcome of cancer (P =.95). No significant differences were observed between the risk of cancer between men and women, or when assessed for higher (20 ng/mL or higher) or lower vitamin D levels.

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The authors concluded that “we showed that monthly high-dose vitamin D supplementation without calcium for up to 4 years is not associated with cancer prevention. Further research is required to study the influence of daily or weekly doses of vitamin D on the risk of cancer for longer periods of time.”


Scragg R, Khaw KT, Loop L, et al. Monthly high-dose vitamin D supplementation and cancer risk [published online July 19, 2018]. JAMA Oncol. doi: 10.1001/jamaoncol.2018.2178