While previous studies have reported an increased incidence of CVD among individuals with low vitamin D status, to date, RCTs involving vitamin D supplementation have not found an effect, possibly because of using too low a dose of vitamin D, said researchers led by Dr Robert Scragg, from the University of Auckland, New Zealand.
In the new RCT study, which lasted for 3.3 years, the researchers randomly assigned adults (age 50 to 84 years) into two groups. Group one consisted of 2,558 participants who received oral vitamin D3 – an initial dose of 200,000 IU, followed by monthly doses of 100,000 IU.
Group two, with 2,552 participants was given a placebo.
“The results of this large population-based randomised clinical trial (RCT) indicate that vitamin supplementation given in the dose and frequency we used does not prevent CVD, and the findings are consistent with previous RCTs of vitamin D supplementation and mendelian randomisation studies,” they wrote in the Journal of the American Medical Association.
“However, it remains possible that monthly doses of vitamin D are less effective in preventing disease than daily or weekly doses.”
Vitamin D deficient
The average age of the participants was 66 years, with 25% vitamin D deficient.
In a random sample of 438 participants during the supplementation period of both vitamin and placebo, the vitamin D status or 25(OH)D level of group one was greater than 20 ng/mL, which was higher compared to the placebo group.
However, participants from the vitamin D group still developed CVD during the median period of 3.3 years.
“Cardiovascular disease occurred in 303 participants (11.8%) in the vitamin D group and 293 participants (11.5%) in the placebo group,” the researchers wrote.
“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.”
Thus, the results concluded that monthly high-dose vitamin D supplementation does not prevent CVD.
“The effects of daily or weekly dosing on CVD risk still require further study,” researchers concluded.
Source: Journal of the American Medical Association
“Effect of monthly high-dose vitamin D supplementation on cardiovascular disease in the vitamin D assessment study a randomised clinical trial”
Authors: Robert Scragg; Alistair Stewart et al.