Date: 20 Aug 1994 07:47:38 -0700 From: taltar@vertigo.helix.net (Ted Altar) Subject: What is a Vitamin? (repost) Newsgroups: rec.food.veg Organization: Helix Internet Lines: 172 WHAT IS A VITAMIN? Ted Altar A. Preamble B. A Proposed Definition C. Is "Vitamin D" Really A "Vitamin?" D. References A. PREAMBLE We all know what vitamins are, right? This common everyday generic term used to refer to a special class of dietary essentials, but these essentials are quite a disparate group "with little in common with each other in either their chemistry or their metabolic functions" (1). Another recent text tells us that for the most part vitamins "are not related chemically and differ in their physiologic roles (2). So what defines a vitamin? The term "vitamin" comes from Polish biochemish Casmir Funk who generalized from his findings on the chemical nature of "vital amines", substances necessary for life (like that of his own discovered substance isolated from rice polishing and which served to have an anitberiberi property). Well, it turns out that this generic descriptor no longer holds as many of the "accessory factors" associated with diets are not all nitrogenous. In fact, what we have now is a chemically heterogeneous group. Consequently, the "e" on "vitamine" was dropped since only a few of the essential substances were found to be amines. Maybe we should be not surprise that the term "vitamin" has been variously defined. The growing understanding of what vitamin does has shown them to have a variety of functions and that vitamin activity may be found in closely related compounds known as "VITAMERS". For example, vitamin A has several seemingly unrelated functions and encompasses not only "retinol" but also "retinal" and "retinoic acid". Also, for instance, some carotenoids can be metabolized to yield the metabolically active form of vitamin A and this would be called PRO-VITAMIN. Life is complicated. B. A PROPOSED DEFINITION Well, maybe the most explicit set of definitional criteria for the term, "vitamin", are those stated by Gerald Combs in his definitive text on vitamins (3) (i) a vitamin is an ORGANIC COMPOUND distinct from fats, carbohydrates and proteins (ii) a vitamin is a NATURAL COMPONENT OF FOODS where it is usually present in minute amounts (iii) a vitam is essentail, also usually in minute amounts, for NORMAL PSHYSIOLOGICAL FUNCTION (i.e., maintenance, growth, development and/or reproduction). (iv) a vitamin causes, but its absence or under- utilization, a SPECIFIC DEFICIENCY SYNDROME (v) a vitamin is NOT SYNTHESIZED BY THE HOST in amounts adequate to meet normal physiological needs. This is a useful definition as it does serve , if only by stipulation, to distinguish vitamins from amino acids, fatty acids and minerals. Notwithstanding this being an useful and explictly well stated set of defining criteria, note the following discrepancies that Combs (3) himself observes: 1. Most animal species have the ability to synthesize ascorbic acid. Only those few which lack the enzyme l- gluonolactone oxidase (e.g., the guinuea pig, humans) cannot; only for them can absorbic acid properly be called VITAMIN C. 2. Individuals exposed to modes amounts of sunlight can produce adequate amounts of cholecalciferol wich for them functions as a hormone. Only individuals without sufficient expose to ultraviolet light (e.g., livestock raised in indoor confinement, people spending most of their days indors) require a dietary source of VITAMIN D. 3. Most animal species have the metabolic capacity to synthesize choline; however (e.g., the chik, the rat) may not be able to enploy that capacity if they are fed insufficient amounts of methyl-donor compounds. In addition some (e.g., the chick) do not develop that capacity fully until several weeks of age. Thus, for the young chik and for individuals of other species fed diets providing limit methyl groups, CHOLINE is a vitamin. 4. All animal speciies can synthesize nicotinic acid mononucleotide (MMN) from amino acid tryptophan. Only those for which this metabolic conversion is particualry inefficient (e.g., the cat, fishes) and others fed low levels of tryptophan require a deitary source of NIACIN. Hence, the term "vitamin" needs to be understood as also relative to the animal species, stage of development, diet or nutritional status, and physical environmental conditions. Generally, the term vitamin is restricted to those substances required by higher organisms, hence the example above of CHOLINE has instead been referred to as a "quasi-vitamin". Some thirteen sustances or groups of stances are generally referred to as "vitamins". Now, let us return to the "vitamin D" debate. C. IS "VITAMIN D" REALLY A "VITAMIN?" "When a corned vessel is no longer a corned vessel should we still call it a cornred vessel?" Confucious Now that we have seen that the term "vitamin"is an evolving term, one that is not permanently written in stone or in the pharmacist's compendium, then it no surprise that some substances once called "vitamins" are no longer referred to as such, and that as knowledge advances we may well see more than 13 substances so designated as vitamines. Similarly, we should not preclude seeing vitamin D reclassified as a non-vitamin. The prevalence of rickets, the disease of growing bones, which is manifest as deformation of long bones (e.g., bowed legs, knock kees, curature of the upper and/or lower arms), swollen joints and/or enlarged heads in children, is generally associated with urbanization and industrialization of human societies. Its appearance on a wide scale was more recent and more restricted geographically than that of either scurvy or beriberi. The first written account of the disease is believed to be that of Daniel Whistler who wrote on the subject in his medical thesis at oxford University in 1645. A complete description of the disease was published shortly thereafter (in 1650) by the Francis Glisson, os it is clear that by the middle of the seventeenth century rickets had become a public health problem in England. However, rickets appears not to have affected earlier societies, at least on such a scale. Studies in the late 1800's by the English physcial T.A. Palm showed that mummified remains of Egyptian dead bore no sings of the disease. By the latter part of the century, the incidence of rickets among children in London exceeded on-third; by the turn of the centry, estimates ofprevalence were as high as 80% and rickets had become known as the "the english disease". D. REFERENCES 1. D. A. Bender (1992). NUTRITIONAL BIOCHEMISTRY OF THE VITAMINS. [Cambridge U. Pr.] 2. Hunt & Groff (1990) ADVANCED NUTRITION AND HUMAN METABOLISM [West publishing comany] 3. Gerald Combs (1992). THE VITAMINS: FUNDAMENTAL ASPECTS IN NUTRITION AND HEALTH [Academic Press]