Traditional vitamins were discovered during the first half of the last century. There was an initial association between diet and health status that led early researchers to identify these essential nutrients. Until identified and labeled as vitamins, these chemicals were called “unidentified growth factors”. That term is still used today.
The term “vitamin” is specific for animal species, stage of development, and/or particular conditions of the physical environment and diet. For example, most primates (other than humans) can make vitamin C, so for them, it is not a vitamin. Guinea pigs, like humans, cannot make vitamin C, which is why they became so popular in research.
Of course, some of our traditional vitamins are not really vitamins. Vitamin D is a hormone not a vitamin, and is manufactured by skin cells when exposed to sunlight.
The quasi-vitamins meet the criteria of a vitamin for only a few species or only under certain conditions, and are not accorded the full status of a vitamin. Under the heading of only a few species are choline, carnitine, and inositol.
Choline is required in the diets of young poultry for optimal growth and freedom of leg disorders. It occurs in foods in the form of phosphatidylcholine (also called lecithin). The best food sources are egg yolk, glandular meats (liver, kidney, brain), soy, wheat germ, and peanuts.
