VITAMIN D FORMS: A brief summary
Three Principal forms of Vitamin D discussed in scientific research
- Parent Form: Vitamin D3, or Cholecalciferol, the form made in the skin.
- Inactive Form: 25OHD, or Calcifediol is converted by the liver, considered the storage form of Vitamin D, the form most frequently tested and measured for Vitamin D Levels.
- Active Form: 1,25OH2D, or Calcitriol is converted by the kidneys, until recently was considered the only biologically active form. Calcitriol circulates as a hormone in the blood, where it performs some of its regulating function, and is carried by the bloodstream to other organs and tissues.
Science for some time has taught that Vitamin D is primarily used in the body's endocrine system, where the Parent form is carried to your liver and kidney, converted to other metabolites and then carried to other organs and tissues of your body. Vitamin D3 is metabolized first to 25 hydroxyvitamin D (25OHD), then to what science has previously (and erroneously) taught was the only "active" form 1,25-dihydroxyvitamin D (1,25OH2D). The Parent form of Vitamin D3 was itself thought to be biologically inert. The metabolites were thought to be the more important forms to measure and monitor. Current research has proven this thinking wrong, and is proposing that the circulating concentrations of the Parent Vitamin D3 may be more important due to 1) discovery that Vitamin D3 can be metabolized within other cells and tissues of the body (not just liver and kidneys), and 2) the Parent Vitamin D3 is significantly more absorbable through the cell walls where it is needed. This change has significant implications for the recommendations of Vitamin D supplementation which have yet to be addressed. In summary, infrequent oral supplementation was deemed appropriate under the previous thinking that the body stored 25OHD to be converted to its active form as needed. The current research indicates that a steady and stable supply of all forms of Vitamin D are needed for optimal health. That cannot be achieved with oral supplementation. It can more likely be achieved with transdermal supplementation from a stable and steady supply.
"Circulating vitamin D, the parent compound, likely plays an important physiological role with respect to the vitamin D endocrine/autocrine system . . . .for the optimal functioning of these systems, significant vitamin D should be available on a daily basis to ensure stable circulating concentrations"
Plos One Research article: 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 exert distinct effects on human skeletal muscle function and gene expression
"The distinct direct and indirect effects of 1α,25(OH)2D3 and 25OHD3 respectively on muscle function and gene expression suggest that multiple other factors must be considered when assessing the physiological impact of vitamin D deficiency or supplementation."
"vitamin D is also delivered directly to all tissues of the body. Many of these tissues . . .can convert vitamin D to its active form within the tissue. . . . Vitamin D has a half life in the autocrine system of roughly 24 hours, so in order for it to have a meaningful impact on cellular functions, you need a new supply of it every day."
"The more constant you can keep your vitamin D level the better equipped your body is to fight disease."
Source: GrassrootsHealth Newsletter, January 20, 2016
Dietary Vitamin D and Its Metabolites Non-Genomically Stabilize the Endothelium, study reported on PubMed
"the presumed inactive sterol, D3, is actually a potent and general mediator of endothelial stability at physiologically relevant concentrations"
“Vitamin D3, which is converted into the active form of vitamin D, suppressed protein insolubility in C. elegans and prevented the toxicity caused by human beta-amyloid which is associated with Alzheimer’s disease,” Prof. Lithgow said.
(note it was the "parent" form, Vitamin D3, prior to conversion to the "active" form that provided the benefits observed)
Vitamin D engaged with known longevity genes – it extended median lifespan by 33% and slowed the aging-related misfolding of hundreds of proteins"
“. . . if it’s a more global marker of health or longevity as this paper suggests, that’s a paradigm shift. Now we’re talking about something very different and exciting.”