Robert Scragg, MBBS, PhD
In a study reported in JAMA Oncology, Robert Scragg, MBBS, PhD, of the School of Population Health, University of Auckland, and colleagues found that monthly high-dose vitamin D supplementation, without calcium, was not associated with a reduced risk of developing cancer.
The current analysis is a post hoc analysis of the Vitamin D Assessment (ViDA) study, which assessed the effect of vitamin D supplementation on the incidence of cardiovascular disease. In the double-blind study, 5,110 participants (aged 50 to 84 years) from family practices and community groups in Auckland were randomized between April 2011 and November 2012 to receive vitamin D3 (n = 2,558) or placebo (n = 2,552). Oral vitamin D3 was given in an initial bolus dose of 200,000 IU followed by monthly doses of 100,000 IU, with study treatment continuing for a median of 3.3 years (range = 2.5–4.2 years). Study medication was discontinued in July 2015, and follow-up was completed in December 2015. The post hoc primary outcome was the number of all primary invasive and in situ malignant neoplasms (excluding nonmelanoma skin cancers). Participants had a mean age of 65.9 years, 58% were male, and 83% were of European or another race/ethnicity (96% European ancestry), with the remainder being Polynesian or South Asian.
At baseline, the mean deseasonalized 25-hydroxyvitamin D (25[OH]D) concentration was 26.5 ng/mL. In a random sample of 438 participants, the mean 25(OH)D concentration during follow-up was consistently > 20 ng/mL higher in the vitamin D group than in the placebo group. A total of 328 cancers were reported, with the most common being melanoma in situ (n = 71) and malignant melanoma (n = 55), followed by prostate (n = 64), colorectal (n = 38), breast (n = 36), and lymphoid and hematopoietic cancers (n = 36).
Cancers occurred in 165 participants (6.5%) in the vitamin D group vs 163 (6.4%) in the placebo group (hazard ratio [HR] = 1.01, P = .95). Results were similar in men (HR = 0.96, 95% CI = 0.74–1.25) and women (HR = 1.09, 95% CI = 0.75–1.59) in the 2 groups, as well as in participants with 25(OH)D < 20 ng/mL (HR = 1.01, 95% CI = 0.65– 1.58) or ≥ 20 ng/mL (HR = 1.04, 95% CI = 0.81–1.33).
The investigators concluded, “High-dose vitamin D supplementation prescribed monthly for up to 4 years without calcium may not prevent cancer. This study suggests that daily or weekly dosing for a longer period may require further study.” ■