Vitamin D Overview

Vitamin D is one of the oldest prohormones and has been produced by various life forms for over 750 million years. Decades of controlled research studies have shown that Vitamin D is imperative to mammals and birds for development, growth and maintenance of a healthy body. There are only two ways to receive the amount of Vitamin D necessary for optimal health: sunlight [Ultraviolet B (UVB] exposure or Vitamin D supplementation. There are several forms of Vitamin D that can be monitored, and each plays an important role in maintaining proper health.

Different Forms of Vitamin D:

Cholecalciferol (Vitamin D3)

This is the naturally occurring form of Vitamin D that is made in your skin when exposed to sunlight. Vitamin D is also available as an oral supplement.

Ergocalciferol (Vitamin D2)

Found naturally in mushrooms and other plants. It is also found in supplements, but is not as effective as Vitamin D3 in some species e.g.chicken.

25-Hydroxycholecalciferol [25(OH)D3] a.k.a. calcidiol and 25-hydroxyergocalciferol [25(OH)D2]

These metabolites are prohormones produced in the liver from cholecalciferol and ergocalciferol. The combined concentration of these two metabolites [total 25(OH)D] in the blood is the most useful measurement for determining Vitamin D status.

1,25-dihydroxycholecalciferol [1,25(OH)2D3] a.k.a. calcitriol and 1,25-dihydroxyergocalciferol [1,25(OH)2D2]

These metabolites are produced from 25(OH)D3 and 25(OH)D2 in an endrocine fashion in the kidney, but are also produced in other tissues in a paracrine fashion. They play a vital role in the formation of normal bone and teeth structure, but also have an important role in immune function and cancer prevention.

24,25-dihydroycholecalciferol [24,25(OH)2D3], 24,25-dihydroxyergocalciferol [24,25(OH)2D2], 1,24,25-trihydroxycholecalciferol [1,24,25(OH)3D3] and 1,24,25-trihydroxyergocalciferol 1,24,25(OH)3D2]

These metabolites are produced in many tissues and are generally considered breakdown or inactivation products of 25(OH)D and 1,25(OH)2D. There are genetic mutations that prevent formation of these breakdown products. Preventing the breakdown of 1,25(OH)2D in particular can lead to elevated blood calcium levels and kidney malfunctions.