Principles of Biochemistry Volume 1 - A. Lehninger 1985

Biomolecules
Vitamins and trace elements: their role in enzyme function
Vitamins as essential organic microcomponents of food

Because The Human Body requires only tiny amounts of Vitamins on a daily basis—on the order of milligrams or even micrograms—they can be classified as minor dietary components. In contrast, Macronutrients such as CARBOHYDRATES, Proteins, and Lipids must be consumed in large quantities, as daily requirements range in the hundreds or at least tens of grams. This is because these primary nutrients serve as Energy Sources and raw Materials for synthesizing organic precursors of various cellular components, as well as providing Amino Acids for METABOLISM/35.html">Protein Biosynthesis. Vitamins, on the other hand, are required only in trace amounts because they act as catalysts in various Chemical transformations of dietary macronutrients—collectively known as metabolism. Much like Enzymes, vitamins are present in Tissues at very low concentrations.

Currently, 13 distinct vitamins are known which, alongside essential nutrients like carbohydrates, lipids, and proteins, must be included in the diets of humans and many animal species to ensure normal growth and physiological function. The term "vitamin" was first coined to describe a specific organic dietary micronutrient that prevented beriberi, a deficiency disease once prevalent in populations heavily reliant on polished rice. Because this micronutrient exhibited amine properties, Kazimierz Funk, the Polish biochemist who first isolated the substance in pure form, named it "vitamine," meaning an "amine essential for life." Later, as many other essential organic micronutrients were discovered, it became clear that far from all of them are actually amines.

Virtually all known vitamins are present in the Cells of all animals and the majority of plants and microorganisms, performing identical vital biochemical Functions across them. However, not all of these vitamins are strictly dietary requirements for every animal species. For instance, although Vitamin C must be obtained from food by humans, primates, guinea pigs, and fruit bats, most other animals do not need dietary vitamin C because they possess the enzymes required to synthesize it from a simple precursor like glucose. Consequently, the term vitamin is used today in a broad sense to denote a group of Organic compounds present in cells in very small amounts that are essential for normal cellular function. At the same time, certain organisms lack The ability to synthesize specific vitamins and must therefore acquire them from external sources.