In recent years, the popularity of vitamin D as a dietary supplement has increased significantly, even without a doctor’s prescription. It has been postulated that besides its recognized positive effect on bone metabolism in certain individuals, it also strengthens the immune system and offers protection against atherosclerosis. However, studies suggest that the latter claim may not be true.
During the Covid-19 pandemic, vitamin D, like other remedies and “miracle cures,” was temporarily touted as a preventive aid against severe illness. Yet, in 2021, experts from the German Society of Nutritional Medicine reviewed dozens of scientific studies and concluded: “Currently, there is no evidence to support vitamin D supplementation in individuals with adequate vitamin D levels for the prevention of SARS-CoV-2 infection or the reduction of Covid-19 severity.”
Furthermore, the experts from the German Society of Nutritional Medicine warned against excessive vitamin D supplementation. It should be avoided as it can lead to undesirable side effects such as kidney stones, kidney calcification, and cardiovascular system disorders. In February of this year, the Austrian Society of Bone and Mineral Metabolism (ÖGKM) stated that vitamin D supplementation cannot be recommended for all healthy individuals of any age.
Clinical studies on the use of vitamin D supplements for preventing cardiovascular diseases have consistently yielded negative results. The most recent example was published in the prestigious British Medical Journal (DOI:10.1136/bmj-2023-075230). Briedie Thompson, from the Public Health Program in Herston, Queensland, Australia, along with her Australian co-authors, conducted a large placebo-controlled study involving 21,316 participants aged 60 to 84 between 2014 and 2020. After random selection, 10,662 participants received 60,000 International Units of vitamin D3 once a month, while 10,653 participants took a placebo tablet once a month for five years.
The primary research objective was to examine the effect of vitamin D intake on severe cardiovascular events such as heart attacks, strokes, and the need for bypass surgery or cardiac catheterization. The data from 21,302 individuals were analyzed, revealing that the frequency of such acute illnesses was six percent in the group taking vitamin D and 6.6 percent in the placebo group. The difference was not statistically significant and could have occurred by chance.
Only when considering the frequency of heart attacks alone, there was a statistically significant difference of 19 percent fewer hospital admissions in the vitamin D group. However, strictly speaking, this was not the main focus of the investigation. There was no significant difference between the two groups regarding the need for oxygen supply restoration to the heart due to coronary artery stenosis (bypass or catheter intervention) and the occurrence of strokes.
According to the German Medical Journal, a meta-analysis of vitamin D studies involving more than 83,000 participants was published in the respected journal of the American Medical Association (JAMA) in 2019. It showed no effect of vitamin D on the incidence of strokes, heart attacks, or cardiovascular deaths overall (DOI:10.1001/jamacardio.2019.1870). Similarly, in 2019, US researchers conducted a study with 25,871 participants over a six-year observation period, comparing the daily intake of vitamin D or placebo, which was published in the New England Journal of Medicine (DOI:10.1056/NEJMoa1809944). The authors wrote, “Supplementation with vitamin D did not result in a lower incidence of invasive cancer or cardiovascular diseases compared to the placebo.” The research project was funded by the National Institutes of Health (NIH) in the United States.