Vitamin D is different from vitamin D-3. Vitamin D itself is a category of fat-soluble vitamins found in a handful of foods including fish, eggs and organ meats. The type of vitamin D found in fish and eggs is called D-2, or ergocalciferol. Organ meats contain the D-3 form, or cholecalcifeol -- the variant synthesized by human skin exposed to UV. Both D-2 and D-3 are referred to as vitamin D, although they are very different in potency and metabolism.
Vitamin D3
Cholecalciferol is the naturally occurring form that converts to calcidiol or 25-hydroxyvitamin D when ingested. Vitamin D-3 is the most important form because calcidiol is a prohormone involved in many metabolic processes. Vitamin D-3 receptors are found in most organs including the brain, prostate gland, mammary glands, heart and skin. Vitamin D-3 receptors are also important for regulating inflammatory processes and immune function.
Calcidiol vs Calcitriol
Calcidiol is metabolized in the kidneys to produce calcitriol or 1,25-dihydroxyvitamin D. Calcitriol is the most potent steroid hormone manufactured from vitamin D-3. Steroid hormones regulate the growth and function of the sex organs. The August 2008 issue of "The American Journal of Clinical Nutrition" discusses the critical role of calcitriol in bone mineralization and calcium regulation. In addition, there are 36 different tissues with receptor cells for calcitriol that represents the 36 places where body functions can go wrong in the event of deficiency.
Vitamin D2
The researchers reporting in the journal article explain that for the past six decades, the scientific literature wrongly claimed that D-3 and D-2 have equivalent biological roles in the human body; however, recent research demonstrates that D-2 is less than one-third as potent as D-3 and is significantly less biologically active than D-3. The differences between the two prompted the authors to call for the use of D-2 in dietary supplements to be discontinued. Vitamin D-2 supplements are manufactured by irradiating plant sterols, while D-3 supplements are made by extracting the naturally occurring form from animal sources.
Blood Serum Vitamin D
Blood serum levels of vitamin D are measured when deficiency is expected or when patients suffer from symptoms of diseases involving energy metabolism. Vitamin D-3 plays a pivotal role in fat metabolism and deficiency is the first step in diagnosing many diseases involving energy production, including kidney disease.
References
- "American Journal of Clinical Nutrition"; The urgent need to recommend an intake of vitamin D that is effective; R. Veith, H. Bischoff-Ferrari, B. Boucher, et. al.; March 2007
- "American Journal of Clinical Nutrition"; From vitamin D to hormone D: fundamentals of the vitamin D endocrine system; A. Norman, August, 2008
- Clincial Journal of the American Society of Nephrology"; Vitamin D and kidney disease; A. Al-Badr, K. Martin; September, 2008.
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