Mito
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Bioavailability of Different Vitamin D Oral Supplements in Laboratory Animal Model
“Anyone sincerely interested in nutrition should be concerned that officially mandated nutritional committee reports for both North America and Europe now state that “Vitamin D is a hormone” [8], or that “Vitamin D is more like a hormone” than a vitamin [9]. This reflects confusion that has arisen because some medical dictionaries define a vitamin as an organic micronutrient that must only be present in the diet, this is a feature that certainly does not reflect the true meaning of the term, vitamin, as coined by Funk [10]. The only requirement of a true vitamin is that it is an organic micro-nutrient whose lack in the diet may result in deficiency disease [10,11]. Vitamin D is not alone as a vitamin attainable by other than dietary means, since niacin can also be synthesized, and vitamin A can be generated in the body from betacarotene.
By itself, a perceived inadequacy of the term, vitamin, could never have created a default situation where a molecule would come to be regarded as a hormone. However, the realization that the kidney functions as a classic endocrine gland, to produce the calcium-regulating hormone, calcitriol, opened the door for some to start referring to Vitamin D as a hormone. Adherents of the Vitamin D is a hormone concept never offer a full explanation of the logic for it. One fallback position for adherents is to state, “Vitamin D is a prohormone”. This is also not valid. A prohormone refers to a committed intra-glandular precursor of a hormone. The most notable examples of pro-hormones are pro-PTH and pro-insulin.
For most of the 20th century, there was no debate that Vitamin D was a nutrient. It was “the sunshine vitamin”, and I contend that we should maintain that perspective. A focus on a poor definition of the word, vitamin, in some dictionaries is no excuse to allow the misconception to continue, that Vitamin D might be regarded as a hormone instead of a nutrient. For reference, more rigorous definitions of words pertinent to vitamin and hormone are presented in Table 1. It should be evident from this that Vitamin D is no more a hormone than cholesterol is—both are the structural raw material that one or more hormones are made from. Vitamin D is a vitamin in the truest sense of the word, because “insufficient amounts in the diet may cause deficiency diseases”.
Why “Vitamin D” is not a hormone, and not a synonym for 1,25-dihydroxy-vitamin D, its analogs or deltanoids - ScienceDirect
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