Hypertension, or high blood pressure, can lead to heart disease and stroke. Approximately two thirds of American adults are affected by hypertension or prehypertension. In 2013, 360,000 American deaths included hypertension as a primary or contributing cause.
Individuals can reduce their risk of developing hypertension by improving their diets, increasing physical activity and minimizing alcohol consumption. In recent years, researchers hypothesized that maintaining a healthy vitamin D status may also reduce the risk of hypertension. This hypothesis was proposed in 1986 after Resnick and colleagues discovered a continuous significant association between active vitamin D levels and renin levels. 
Renin is an enzyme that plays a vital role in the renin-angiotensin aldosterone system, or what is known as RAAS. The RAAS regulates blood pressure and fluid balance through an intricate feedback process. Decreased blood flow to the kidneys stimulates renin secretion. Then, renin converts a protein called angiotensinogen into angiotensin I. An enzyme called ACE converts angiotensin I into angiotensin II. Lastly, the presence of angiotensin II cues the secretion of aldosterone. Aldosterone works by reabsorbing water and salt in the kidneys and constricting small arteries, leading to an increase in blood pressure.
High blood pressure may be treated with ACE inhibitors, a type of medication that stops the conversion of angiotensin I into angiotensin II. Thus, ACE inhibitors prevent the increase in blood pressure caused by aldosterone.
Due to Resnick’s discovery, researchers became interested in the effects of vitamin D on RAAS. Zhang and colleagues later found that vitamin D receptor knockout mice experienced a significant increase in angiotensin II and renin levels. A cohort study went on to find that low vitamin D levels were related to higher levels of the hormones involved in RAAS.
In a new study, researchers wanted to find out the effects of vitamin D supplementation on aldosterone levels in adults with hypertension. A total of 188 hypertensive patients with vitamin D levels less than 30 ng/ml were enrolled into the study. The patients were randomized to receive either 2800 IU of vitamin D3 or placebo daily for 54 days. Vitamin D levels and plasma aldosterone concentration (PAC) were measured before and after treatment. The researchers also collected information regarding medication use and adjusted the results for baseline differences in those who took ACE inhibitors. Here is what the researchers found:
The researchers concluded,
“The present investigation is the first RCT to describe a significant reduction of plasma aldosterone by vitamin D supplementation compared with placebo in patients with arterial hypertension.”
The results support the hypothesis that vitamin D supplementation may help manage hypertension. The study utilized the gold standard of research, a randomized controlled trial. Due to the powerful study design, the researchers were able to prove causation. However, it is important to note that changes in blood pressure was not measured. Thus, as the writers stated, “the question of whether the significant reduction of PAC is of clinical relevance arises.” The researchers also point out that there was a low prevalence of patients with vitamin D deficiency below 20 ng/ml, and those with severe vitamin D deficiency would likely gain the most benefits from vitamin D supplementation.
Tovey, A. Study provides evidence to support vitamin D’s role in treating high blood pressure. The Vitamin D Council Blog & Newsletter, 2016.
 Tomaschitz A, Pilz S, Ritz E, et al. Independent association between 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D and the renin-angiotensin system: the Ludwigshafen Risk and Cardiovascular Health (LURIC) study. Clinica Chimica Acta, 2010.