, including mortality linked to cardiovascular disease, new results from a large, placebo-controlled trial show.
“The take-home message is that routine vitamin D supplementation, irrespective of the dosing regimen, is unlikely to be beneficial in a population with a low prevalence of vitamin D deficiency,” first author Rachel E. Neale, PhD, of the Population Health Department, QIMR Berghofer Medical Research Institute, in Brisbane, Australia, told this news organization.
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Despite extensive previous research on vitamin D supplementation, “mortality has not been the primary outcome in any previous large trial of high-dose vitamin D supplementation,” Dr. Neale and coauthors noted. The results, published online in Lancet Diabetes & Endocrinology, are from the D-Health trial.
With more than 20,000 participants, this is the largest intermittent-dosing trial to date, the authors noted. The primary outcome was all-cause mortality.
In an accompanying editorial, Inez Schoenmakers, PhD, noted that “the findings [are] highly relevant for population policy, owing to the study’s population-based design, large scale, and long duration.”
This new “research contributes to the concept that improving vitamin D status with supplementation in a mostly vitamin D-replete older population does not influence all-cause mortality,” Dr. Schoenmakers, of the Faculty of Medicine and Health Sciences, University of East Anglia, Norwich, England, said in an interview.
“This is not dissimilar to research with many other nutrients showing that increasing intake above the adequate intake has no further health benefits,” she added.
D-Health Trial
The D-Health Trial involved 21,315 participants in Australia, enrolled between February 2014 and June 2015, who had not been screened for vitamin D deficiency but were largely considered to be vitamin D replete. They were a mean age of 69.3 years and 54% were men.
Participants were randomized 1:1 to a once-monthly oral vitamin D3 supplementation of 60,000 IU (n = 10,662) or a placebo capsule (n = 10,653).
They were permitted to take up to 2,000 IU/day of supplemental vitamin D in addition to the study protocol and had no history of kidney stones, hypercalcemia, hyperparathyroidism, osteomalacia, or sarcoidosis.
Over a median follow-up of 5.7 years, there were 1,100 deaths: 562 in the vitamin D group (5.3%) and 538 in the placebo group (5.1%). With a hazard ratio (HR) for all-cause mortality of 1.04, the difference was not significant (P = .47).
There were also no significant differences in terms of mortality from cardiovascular disease (HR, 0.96; P = .77), cancer (HR, 1.15; P = .13), or other causes (HR, 0.83; P = .15).
Rates of total adverse events between the two groups, including hypercalcemia and kidney stones, were similar.
An exploratory analysis excluding the first 2 years of follow-up in fact showed a numerically higher hazard ratio for cancer mortality in the vitamin D group versus no supplementation (HR, 1.24; P = .05). However, the authors noted that the effect was “not apparent when the analysis was restricted to deaths that were coded by the study team and not officially coded.”
Nevertheless, “our findings, from a large study in an unscreened population, give pause to earlier reports that vitamin D supplements might reduce cancer mortality,” they underscored.
Retention and adherence in the study were high, each exceeding 80%. Although blood samples were not collected at baseline, samples from 3,943 randomly sampled participants during follow-up showed mean serum 25-hydroxy-vitamin D concentrations of 77 nmol/L in the placebo group and 115 nmol/L in the vitamin D group, both within the normal range of 50-125 nmol/L.