The vitamin D receptor (VDR) is present in virtually all cells and tissues. It has been estimated that 3% to 10% of all genes are under the direct or indirect control of 1,25(OH)2D3, so the potential effect of vitamin D on the body is very large.
Vitamin D supplementation has no effect on any individual’s cardiovascular event, such as myocardial ischemia, or in the composite cardiovascular end points.
Vitamin D status has no influence on cancer incidence, but supplementation with vitamin D does reduce cancer mortality. This finding is most likely associated with the fact that vitamin D is antiproliferative. We will discuss the antiproliferative aspect of vitamin D when we discuss implant integration.
Vitamin D supplementation for those who are predisposed to diabetes showed no reduction on the incidence of diabetes mellitus (DM). However, when the treatment group was limited to those deficient in vitamin D with a baseline of 25OHD <12 ng/mL (or < 30 nmol/L), the results showed a 62% reduction in the development of DM in the vitamin D group. This is a common finding when studying vitamin D. Giving vitamin D to the general population shows no benefit, but when you locate those who are deficient in vitamin D, supplementation then shows a benefit. The key to this fact is that only 6% of the population in the US is deficient in vitamin D. We will discuss this more in relationship vitamin D status as related to bone health.
Relationship to COVID-19
he reason why vitamin D was tried in the first place was the knowledge that in patients with vitamin D deficiency, it has been found to reduce the risk of respiratory infection. In an individual participant data meta‐analysis of 15 RCTs (randomized clinical trials), daily or weekly supplementation in individuals with vitamin D deficiency, defined as a serum 25OHD level <10 ng/mL, reduced risk of acute respiratory infection by 30% (odds ratio, 0.30; 95% CI, 0.17–0.53). The key here, again, is in order for vitamin D to have any benefit, the patients needed to be deficient in vitamin D and very few healthy people in the US are.
Vitamin D is Produced by UVB Light from the Sun
UVB light (wavelength of approximately 280 to 310 nm) opens the B ring of 7‐dehydrocholesterol, the last step in the synthesis of cholesterol, and generates pre-vitamin D, which undergoes thermally-induced isomerization into vitamin D3 before being transferred into the circulation by binding to the serum vitamin D binding protein (DBP). From the following graph, you can see that vitamin D production from sun exposure is very efficient and only a small amount of exposure is required to maximize vitamin D production:
Am J Clin Nutr. 2008 Aug;88(2):570S-577S. doi: 10.1093/ajcn/88.2.570S.