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High-dose vitamin D may not prevent cancer
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Individuals who received monthly high concentrations of vitamin D without calcium did not appear to have lower risk for cancer, according to findings from a post-hoc analysis of the Vitamin D Assessment study.
“The results of this large randomized clinical trial suggest that monthly high-dose vitamin D supplementation is not associated with reductions in cancer incidence or cancer mortality in people selected from the community in New Zealand,” Robert Scragg, MBBS, PhD, from the school of population health at University of Auckland in New Zealand, and colleagues wrote.
Ecological studies have reported inverse associations between sun exposure, source of vitamin D and incidence of several types of cancer.
However, randomized clinical trials of vitamin D supplementation for have shown conflicting impact on cancer risk.
Scragg and colleagues randomly assigned 5,110 individuals (mean age, 65.9 years; 58.1% men) from family practices and community groups throughout Auckland, New Zealand to receive vitamin D3 (n = 2,558) — at an initial bolus dose of 200,000 IU followed by monthly doses of 100,000 IU — or placebo (n = 2,552) for a median of 3.3 years (range, 2.5-4.2).
Investigators chose a monthly 100,000-IU dose of vitamin D3 based on previous pharmacokinetic research showing that dosage preserved 25-hydroxyvitamin D concentrations higher than 35 ng/mL for a month after consumed.
Patients received vitamin D3 or placebo via mail with a page to self-report adherence, which researchers used to monitor retention.
Among 5,108 participants included in the final analysis, 83.3% had European descent or another race/ethnicity, with the remainder being Polynesian or South Asian; 6.3% reported using tobacco and 42.5% were former smokers; and 23.8% reported being previously told by a physician that they had cancer.
Incidence of all primary invasive and in situ malignant neoplasms, with the exception of nonmelanoma skin cancers, diagnosed from baseline through discontinuation of medicine on July 31, 2015, served as the study’s post hoc primary outcome.
Patients had a mean baseline 25-hydroxyvitamin D concentration of 25.3 ng/mL (standard deviation [SD], 9.5 ng/mL) and deseasonalized concentration of 26.5 ng/mL (SD, 9 ng/mL).
Within 2 months from baseline, 98% of participants confirmed by questionnaire that they had initiated taking vitamin D or placebo.
During the last 5 months of active follow-up, 86.6% of participants remained involved in the trial, as indicated by 80.9% of participants who returned the final questionnaire and an additional 5.7% who returned the penultimate questionnaire.
Adherence to taking vitamin D or placebo reported in the home questionnaires was 85,280 capsules over 100,535 person-months (84.8%) among individuals who received vitamin D3 and 83,387 capsules over 100,401 person-months (83.1%) among individuals who received placebo.
In a random sample of 438 participants who provided blood samples, researchers observed mean vitamin D3 concentration that ranged from 48 ng/mL to 54 ng/mL in the vitamin D group, which was consistently 20 ng/mL higher than those of the placebo group.
Overall, 328 participants developed cancer — 259 invasive and 69 in situ malignant neoplasms —which included 165 participants in the vitamin D3 group and 163 in the placebo group (adjusted HR = 1.01; 95% CI, 0.81-1.25).
Vitamin D supplementation did not demonstrate a protective effect against cancer for men (HR = 0.96; 95% CI,0.74-1.25) or women (HR = 1.09; 95% CI, 0.75-1.59).
Researchers did not observe a difference among participants with less than 20 ng/mL vitamin D3 concentration (HR = 1.01; 95% CI, 0.65-1.58) compared with 20 ng/mL or higher vitamin D3 concentration (HR = 1.04; 95% CI, 0.81-1.33).
The researchers noted that cancer incidence results appeared consistent with findings from previous randomized clinical trials of community samples in the United States, which reported an HR of 0.98 (95% CI, 0.90-1.05), and Great Britain, which reported an HR of 1.09 (95% CI, 0.86-1.36).
“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,” the researchers wrote. – by Melinda Stevens
Disclosures: The researchers report no relevant financial disclosures.
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