Results from a recent large meta-analysis suggest that vitamin D supplementation is ineffective in lowering blood pressure.
Observational research has provided strong evidence of an association between low vitamin D levels and high blood pressure or hypertension. Researchers have proposed various biological mechanisms to explain this relationship.
Vitamin D receptors have been discovered on endothelial cells, smooth muscle cells, and myocytes, all of which are found in the cardiovascular system. Vitamin D has also been shown to reduce the production of a class of anti-inflammatory proteins known as cytokines, which may contribute to the development of hypertension. Additionally, vitamin D reduces the expression of renin, an enzyme that increases blood pressure within the renin-angiotensin-aldosterone system.
However, intervention trials have produced mixed results with regards to the effect of vitamin D on hypertension. In order to better our understanding of the effects of vitamin D supplementation on blood pressure, researchers recently conducted a meta-analysis of 46 randomized controlled trials.
Researchers only included trials if they measured baseline vitamin D levels and evaluated blood pressure reduction. All studies included an intervention of at least 4 weeks. They looked at trials that used vitamin D2, vitamin D3, activated vitamin D, or vitamin D analogs.
After analyzing the data from 46 trials, totaling 4,541 participants, researchers found no effect of vitamin D supplementation on either systolic or diastolic blood pressure.
The researchers gathered data sets of individual patients to investigate the effect of vitamin D supplementation on groups who would most likely benefit, such as participants with low vitamin D levels and high blood pressure. They looked at data from 27 trials and found similar results with an average of 0.4 decrease in systolic blood pressure (p = 0.27) and a decrease of 0.2 in diastolic blood pressure (p = 0.38). In subgroup analyses, no baseline factor predicted a better response to therapy.
“Our analysis found no evidence of BP reduction by supplementation with vitamin D or vitamin D analogues, a result that was consistent between the trial-level and individual patient data analyses.”
The researchers acknowledged the study’s important limitations. All of the studies were relatively small with no study including more than 1,000 patients. Furthermore, not all of the studies were of high quality. More importantly, very few trials targeted patients with hypertension (high blood pressure). Vitamin D may only be helpful in reducing abnormally high blood pressure. Additionally, the researchers noted that most doses were lower than what is required to reach healthy vitamin D levels. Lastly, many of the studies used intermittent doses, which have been research suggests is less effective than daily doses.
This meta-analysis does not provide strong evidence for a lack of an effect of vitamin D on hypertension. Meta-analyses of well-designed randomized controlled trials are needed to reach a consensus on the efficacy of vitamin D supplementation on hypertension. However, before this can occur, more well-designed randomized controlled trials of vitamin D deficient patients with hypertension using 5,000 to 10,000 IU/day need to be conducted.