Calcitriol is the 1,25(OH)-D3 that is usually produced by CYP enzymes in the kidneys, and it is the “active form” of vitamin D. Kidney failure can derail this process, and so patients with kidney failure are often given calcitriol as a supplement. However, a study published in 2006 found it counterproductive for young adults with childhood-onset end-stage renal disease to be given calcitriol supplementation, because calcitriol is taken up by cells in the artery wall and leads to increased artery calcification.21
Basically, vitamin D mobilizes calcium but doesn’t control where calcium goes. I believe that sulfate deficiency in the vasculature drives a conversion of the smooth muscle cells into bone-like cells, and this causes them to actively take up calcium and phosphate. Vitamin D supplements will encourage them to do this faster. Artery calcification is one of the strongest risk factors for cardiovascular disease.
HIGH BLOOD PRESSURE
A paper, apty titled, “Sunlight Has Cardiovascular Benefits Independently of Vitamin D” argued that sunlight is a therapy option for high blood pressure, and important risk factor for cardiovascular disease. A scatter plot showing mean male population blood pressure vs central latitude for large number of countries, reproduced here as Figure 2, demonstrated a clear linear relationship. The author argued that the reduction in blood pressure is due to sunlight’s stimulation of the release of nitric oxide from the skin.
Figure 2: Population blood pressure (BP) correlates with latitude. Each point represents a country. Male systolic population BP is plotted against the latitude of the geographical midpoint of each country. BP values are from 1980 MRC-HPA data. See Weller, 2016 for details.2