Can vitamin D really improve cardiovascular health?

Results from the D-Health randomized clinical trial show that a monthly intake of 60,000 IU of vitamin D for five years did not significantly reduce the risk of major cardiovascular events in 21,302 participants aged 60 and over. Overall, 6% of participants in the group taking vitamin D experienced a major cardiovascular incident during the trial, such as stroke, myocardial infarction or coronary revascularization, compared to 6.6% in the group placebo, with a 95% confidence interval. After statistical adjustment, the difference between the two groups was 5.8 incidents per 1,000 participants. Read: Are kidney stones sweet on sugar? “The confidence intervals are often much wider, they are the most precise that it is possible to obtain. I'd like to think we'll get even more accurate results in the future, but I don't expect we will," says Rachel Neale, senior research fellow at the Queensland Institute of Medical Research and co-author of the study. Nevertheless, the data, published June 28 in the British Medical Journal, reveals a slight decrease in the risk of myocardial infarction (19%) and coronary revascularization (11%) in the group taking vitamin D. No difference has been noted regarding the risk of stroke. "Myocardial infarction is explained by a mechanism on which vitamin D is more likely to have an effect," unlike stroke, says the researcher. Read: Exercise may or may not help you lose weight and keep it off—here’s the evidence for both sides of the debate A protective effect? According to the World Health Organization (WHO), heart disease and stroke were among the leading causes of death worldwide in 2019, and will continue to gain ground in the years to come. “We are interested in vitamin D because many studies have shown that people who have low levels of it in their blood are more at risk of cardiovascular events, but we do not know if this is causal, because people in this situation tend to be less active,” says Neale. Previous observational studies have noted an inverse association between calcitriol, the hormonally active form of vitamin D, and cardiovascular disease. Vitamin D is converted in the liver to 25-hydroxyvitamin D, then in the kidneys to calcitriol, which reduces inflammation, regulates the renin-angiotensin-aldosterone system and inhibits the proliferation of smooth muscle cells. In the D-Health clinical trial, serum 25-hydroxyvitamin D, a measure of vitamin status, was 77 nmol/L in the placebo group, compared to 115 nmol/L in the group taking vitamin D. "If [vitamin D] does reduce the risk of cardiovascular disease, it's a simple and relatively cheap intervention that could be used," says Neale. An uncertain future for research The randomized clinical trials ViDA and VITAL had concluded that vitamin D did not prevent cardiovascular accidents. Neale says she was not surprised that D-Health also ran into this wall, but the research paper notes that it would be also be premature to conclude that vitamin D does not alter the risk of cardiovascular disease. The team remains hopeful given the results obtained in a subgroup of participants. She observed that those who received statins or other heart treatments at the start of the trial would have shown a better protective effect from vitamin D. There could have been an interaction between vitamin D and these treatments, but this is the least likely hypothesis, according to Neale. “My hypothesis is that people who are already at high risk have more room for improvement,” she explains. The researcher thinks that other large-scale clinical trials around the world on vitamin D could reanalyze their data taking into account the taking of these drugs by their participants, and combine them with those of D-Health. Nevertheless, she says her team does not intend to continue research in this direction for the moment. She even expects that other large-scale clinical trials on vitamin D will not see the light of day given the virtual impasse in which the researchers find themselves. Doctors and governments must now make decisions based on public interest and the very limited evidence of vitamin D's effects on cardiovascular health, she says. “We are going to have to live in the face of uncertainty when making decisions about vitamin D supplementation,” she adds. "I don't think there will ever be a pill that will do as good a job as maintaining an active lifestyle and good nutrition." This article has been translated from its original French and first appeared on our sister site Profession Santé.

Can vitamin D really improve cardiovascular health?

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