Vitamin D — the basics and a little more!
By Dr. Emily Brown Reeves. PhD. CNS.
Vitamin D exists as a preprohormone, prohormone, and hormone in the body. The preprohormone has two forms cholecalciferol (Vitamin D3) and ergocalciferol (Vitamin D2).
Food sources of Vitamin D3 include cod liver oil, salmon, swordfish, tuna, liver, and eggs. Vitamin D2 is found in mushrooms grown in UV light or it can also be found in fortified foods, and dietary supplements. When considering supplementation one should realize that Vitamin D2 is cleared more quickly from the circulation than Vitamin D3 and therefore may be inferior to Vitamin D3 for repletion purposes. Vitamin D2 and Vitamin D3 are both converted to the prohormone and therefore contributions from both are assessed by the standard clinical measurement of 25-hydroxyvitamin D.
References
Hollis BW. Circulating 25-hydroxyvitamin D levels indicative of vitamin D sufficiency: implications for establishing a new effective dietary intake recommendation for vitamin D. J Nutr. 2005;135(2):317-322.
Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911-1930.
Bikle DD. Vitamin D metabolism, mechanism of action, and clinical applications. Chem Biol. 2014;21(3):319-329.