++
Vitamins are organic compounds required in very small amounts (from a few micrograms to a few milligrams daily) to prevent clinical deficiency and deterioration in health, growth and reproduction. A distinct feature of vitamins is that the human body is not able to synthesise them. Classification of vitamins is based on their relative solubility: fat-soluble vitamins (A, D, E and K) are more soluble in organic solvents, and water-soluble vitamins (B-complex, beta-carotene and C) in water.
++
Most vitamins participate in processes related to muscle contractions and energy expenditure (see Table 12.1). Vitamins of the B-complex group (e.g. thiamin, riboflavin, vitamin B6, niacin, biotin, pantothenic acid) act as cofactors for enzymes regulating glycolysis, citric acid cycle, oxidative phosphorylation, b-oxidation (breakdown of fatty acids) and amino acid degradation. Folic acid and vitamin B12 are needed for haemoglobin synthesis. Ascorbic acid (vitamin C) activates an enzyme-regulating biosynthesis of carnitine, which is necessary for fatty acid transportation from cell cytosol into mitochondria. Finally, antioxidant vitamins (mainly vitamins C and E) and some minerals participate in the buffer system against free radicals, which are produced by increased energy turnover.
++++
Minerals are inorganic substances found naturally on the earth. Based on their daily requirements, minerals are usually classified as macrominerals (e.g. sodium, potassium, calcium, phosphorus, magnesium) or trace elements (e.g. iron, zinc, copper, chromium, selenium). The daily dietary requirement for macrominerals is more than 100 mg/d, whereas trace elements are needed in much smaller quantities (less than 20 mg/d).
++
Several minerals and trace elements, such as magnesium, iron, zinc and copper, act as enzyme activators in glycolysis, oxidative phosphorylation and in the system responsible for maintenance of acid-base equilibrium (see Table 12.2). Iron is needed for haemoglobin synthesis. Minerals (electrolytes) also affect muscle contraction.
++