High-dose vitamin D supplementation given monthly does not prevent cardiovascular disease, results of a large randomized trial suggested Wednesday.
People with low vitamin D status have previously been linked to increased incidence of cardiovascular disease, but so far, randomized clinical trials of vitamin D supplementation have not found an effect, possibly because of using too low a dose of vitamin D.
The new study, published in the U.S. journal JAMA Cardiology, included more than 5,100 adults with an average age of 66 years, 25 percent of whom were vitamin D deficient.
These participants were randomly divided into two groups and given either oral vitamin D3 or placebo with an initial dose of 5.0 mg followed by monthly doses of 2.5 mg.
After 3.3 years of follow-up, cardiovascular disease occurred in 303 participants, or 11.8 percent, in the vitamin D group and 293 participants, or 11.5 percent, in the placebo group.
Similar results were seen for participants with vitamin D deficiency at study entry and for other outcomes such as heart attack, angina, heart failure, hypertension, and stroke.
"This result does not support the use of monthly high-dose vitamin D supplementation for this purpose (prevention of cardiovascular disease)," Robert Scragg of the University of Auckland, New Zealand, and colleagues wrote in their study. "The effects of daily or weekly dosing require further study."
Tim Chico, reader in cardiovascular medicine and consultant cardiologist of the University of Sheffield, who was not involved in the study, said this study adds to a large number of others that found disappointing or even harmful effects of vitamin supplementation on a range of diseases, including heart disease and cancer.
"I see a lot of patients who take vitamin supplements in the expectation that this will reduce their risk of disease, and unfortunately I have to tell them that the evidence suggests they are a waste of time and money," Chico said.
Professor Adrian Martineau of the Queen Mary University of London, said this trial does not rule out the possibility that vitamin D might have a role in reducing risk of cardiovascular disease if it were to be given in a different way or to a population with different characteristics.
"The bottom line is that the authors have conclusively shown that this dosing regimen of vitamin D, given to this population, did not prevent cardiovascular disease -- and this is an important null finding," Martineau said.
"However, these results do not rule out a protective effect of daily/weekly dosing in people with low vitamin D levels."