03.18.2015

Vitamin D is everyone’s favorite supplement, but it’s getting no love from the authors of a recent analysis.

No association was found between vitamin D and a lowered blood pressure, found a large meta-analysis, led by Miles Witham, PhD, from the University of Dundee in Scotland.

The findings received widespread media coverage, and some took the opportunity to call for an end to widespread vitamin D supplementation.

David Agus, MD, for example, was asked by Charlie Rose on CBS This Morning if we need vitamin D. “The answer is no,” said Agus. “More and more people are taking it — it’s the second most taken vitamin in the country, behind multivitamins.”

Agus then said that patients should challenge their doctors and ask for data if they’re told they need to take more vitamin D. “We now have to reassess what is normal,” he said. “Nobody should be taking it at the present time, in a normal individual.

Witham and colleagues published their results in JAMA Internal Medicine on March 16. They found that neither systolic blood pressure (treatment effect 0.0, 95% CI minus 0.8-0.8; P=0.97) nor diastolic blood pressure (-0.1, 95% CI minus 0.6-0.5; P=0.84) changed significantly from baseline to follow-up. Included in the analysis were 46 randomized, placebo-controlled trials.

“A clinically significant reduction in BP is unlikely based on the doses of vitamin D studied in this analysis,” wrote the authors, “The lack of effect argues against a role for vitamin D supplementation as a means of BP control in individual patients or as a population-based intervention to reduce BP.”

In addition to looking at study-level data, researchers also looked an individual patient data, and had similar findings, both for systolic BP (-0.5 effect size, 95% CI minus 1.3-0.4; P=0.27) and diastolic BP (0.2, 95% CI minus 0.3-0.7; P=0.38). A subgroup analysis showed that no factors at baseline were predictive of a better response to vitamin D.

“Our use of individual patient data allowed us to examine whether particular subgroups might still benefit from vitamin D supplementation, which previous analyses have not been able to address,” the authors wrote.

All included studies had reported baseline vitamin D levels, as well as a minimum of 4 weeks of intervention, and participants older than 16. In the individual patient analysis, 27 studies were included. The research period spanned from 1966 to 2014.

Almost all of the studies were single-center trials, and most were smaller. None of the studies recruited more than 1,000 patients. An additional limitation was that only a small number of trials targeted patients with hypertension at baseline — “such patients would perhaps be more likely to respond to antihypertensive interventions,” noted the authors.

It’s also possible that vitamin D has a positive effect on cardiovascular health in ways that aren’t captured by the blood pressure measurements used in the studies.

“Although larger, more frequent doses of vitamin D might still have effects on reducing BP, we found no evidence of a dose-response relationship in our analyses,” wrote the authors.