Scragg R, et al. - In this post hoc analysis of the Vitamin D Assessment (ViDA) study—a randomized, double-blind, placebo-controlled trial—that included 5,108 community-dwelling adults aged 50-84 years in Auckland, New Zealand, researchers investigated the association of high-dose vitamin D supplementation with cancer prevention. According to findings, monthly high-dose vitamin D supplementation for up to 4 years without calcium may not prevent cancer and, therefore, should not be used for this purpose.

Methods

• Study participants were enrolled from April 5, 2011, through November 6, 2012, with follow-up completed December 31, 2015.
• Of the 47,905 adults from family practices and 163 adults from community groups who were invited for screening and enrollment, a total of 5,110 meet inclusion criteria and were randomized to receive either vitamin D₃ (n=2,558) or placebo (n=2,552)
• Consent was withdrawn by two participants; thus, the primary analysis included all other participants (n=5,108).
• Intention to treat data analysis was performed.
• Participants were given oral vitamin D₃ in an initial bolus dose of 200,000 IU and followed by monthly doses of 100,000 IU or placebo for a median of 3.3 years (range, 2.5-4.2 years).
• The number of all primary invasive and in situ malignant neoplasms, (excluding nonmelanoma skin cancers) diagnosed from randomization until the study medication was discontinued on July 31, 2015, and was assessed as the post hoc primary outcome.

Results

• Researchers identified mean (SD) baseline deseasonalized 25-hydroxyvitamin D concentration of 26.5 (9.0) ng/mL.
• In a random sample of 438 participants, the mean follow-up 25-hydroxyvitamin D concentration consistently was greater than 20 ng/mL higher in the vitamin D group than in the placebo group
• The primary outcome of cancer comprised 328 total cases of cancer (259 invasive and 69 in situ malignant neoplasms); the vitamin D group had 165 cases of cancer among 2,558 participants (6.5%) vs 163 of 2550 (6.4%) participants in the placebo group, yielding an adjusted hazard ratio of 1.01 (95% CI, 0.81-1.25; P=0.95).