Human Anatomy and Physiology - N. I. Fedyukovich 2003

Metabolism and Energy
Vitamins

Vitamins are Organic compounds characterized by high biological activity and diverse chemical structures. Because The Human Body either cannot synthesize them at all or produces them in insufficient quantities, they must be obtained through diet.

Vitamins comprise various classes of compounds and play a catalytic role in METABOLISM, frequently acting as integral components of enzyme systems. Consequently, vitamins function as essential regulatory agents.

The primary sources of vitamins are foods of PLANT AND ANIMAL origin. In foodstuffs, they may occur in active or inactive forms (provitamins), the latter being converted into active compounds within the body. In addition, certain Vitamins can be synthesized by the intestinal microflora.

Currently, approximately 40 vitamins are known. They are classified into fat-soluble (A, D, E, K, F) and Water-soluble (B₁, B₅, B₆, B₁₂, C, PP, etc.) groups. Fat-soluble vitamins are predominantly found in animal products, vegetable oils, and, to some extent, green leafy vegetables. Water-Soluble Vitamins are mainly supplied by plant-based foods (grains, legumes, vegetables, fresh fruits, and berries) and, to a lesser degree, by animal products; however, animal-derived foods serve as the primary source of nicotinic acid and cyanocobalamin. While some vitamins are resistant to degradation, others lose their activity during storage and food Processing.

An inadequate daily intake of one or more vitamins disrupts metabolism and leads to disease. A reduced dietary intake or impaired Absorption of Vitamins results in hypovitaminosis, whereas their complete absence causes avitaminosis. Avitaminoses manifest as various functional Disorders of the Organism, reflecting the diverse regulatory roles of vitamins. They are involved in The regulation of Intermediary Metabolism and cellular Respiration (B-group vitamins, nicotinic acid); the synthesis of Fatty acids, Steroid Hormones (pantothenic acid), and Nucleic Acids (folic acid, cyanocobalamin); photoreception and reproduction (retinol); Calcium and phosphorus metabolism (calciferols); oxidation-reduction processes (ascorbic acid, tocopherols); as well as hemopoiesis and the synthesis of Blood clotting factors (phylloquinones), among others.

Certain substances exhibit vitamin-like properties, such as Para-aminobenzoic Acid, Inositol, pangamic acid, Vitamin U, and Lipoic Acid.

In many cases, the daily requirement for water-soluble and fat-soluble vitamins ranges from 2 µg (cyanocobalamin) to 50–100 mg (ascorbic acid) and 200 µg (folic acid).

The daily vitamin A requirement for an adult is 1 mg, and the requirement for vitamin D is 100 IU.

It is known that water-soluble vitamins perform antioxidant Functions, whereas fat-soluble vitamins help stabilize Introduction/36.html">Biological Membranes, protecting them against oxidative damage.