Vitamins (name deriving from "amines of life") are: a heterogeneous group of organic substances, indispensable in small quantities for growth and for a correct regulation of the vital activities of the organism.
Vitamins are REGULATORS, they participate in an essential way in metabolism and some constitute the key structure of coenzymes. They do not provide energy and act with specific functions in small doses; usually, human needs are measurable in quantities between micrograms (µg) and milligrams (mg).
Not ALL foods contain all vitamins; some have few "traces" and in others there are only "precursors" (which require the metabolic synthesis of the organism).
Vitamin deficiency leads to avitaminosis (total lack of one or more vitamins) or hypovitaminosis (partial lack of one or more vitamins), while excess sometimes leads to hypervitaminosis (toxic state due to usually pharmacological overdoses).
Vitamins can be identified by nomenclature, by a letter of the alphabet or by reference to chemical characteristics or biological activities. The most common classification is that referring to solubility:
- Water-soluble vitamins (water soluble): Vitamin C (L-ascorbic acid), Vitamin B1 (Thiamine), Vitamin B2 (Riboflavin), Vitamin B5 (Pantothenic acid), Vitamin B6 (Pyridoxine), Vitamin PP (Niacin), Vitamin B12 (Cyanocobalamin ), Vitamin Bc (Folic Acid), Vitamin H (Biotin).
- Vitamins liposolubili (fat soluble): vitamin A, vitamin D, vitamin E, vitamin K, vitamin "F" or essential fatty acids (AGEs).
Which ones are they
The fat-soluble vitamins are A, D, E, K and "F". Let's see them in detail.
Vitamin A (antixeroftalmica)
S are fat-soluble vitamins of group A: vitamin A1 (retinol), vitamin A2 (3-dehydroretinol) and provitamins (Β-carotenes). In animal tissues there are A1 and A2 (also called retinol 1 and 2), while in plants the provitamins are widespread and subsequently converted in animals by the liver. Food sources are yolk, liver, milk and derivatives, butter, yellow and orange or green colored vegetables. The fat-soluble vitamins type A are responsible for the formation and maintenance of epithelia, mucous membranes, bones and teeth, and participate in physical and immune growth; they are also powerful antioxidants; they are absorbed together with lipids and are stored in the liver. The deficiency causes night blindness, compromised cornea (xerophthalmia), reduced growth, tooth breakage and predisposition to tumors. Excess causes: irritability, nausea, vomiting, growth retardation, liver damage, baldness, malformation of the fetus and other symptoms.
Vitamin D (antirachitic)
They are fat-soluble vitamins of group D: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Ergocalciferol is obtained from ergosterol, a molecule of plant origin, while cholecalciferol is of animal origin. At the endogenous level, the synthesis precursor of cholecalciferol is 7-dehydrocholesterol, subsequently transformed in the skin by irradiation of ultraviolet (UV) rays. Cholecalciferol is found in milk, yolk, tuna, salmon and cod liver oil. The fat-soluble vitamins of group D intervene in the regulation of phosphorus (P) and are essential for ossification; much of the portion ingested with food is NOT used (about 70%) while the most important source is always the endogenous synthesis in the skin. Vitamin D deficiency in children leads to rickets, osteomalacia in adults and possibly osteoporosis in the elderly. Excess causes nausea, weight loss, irritability, growth retardation, hypercalcemia (calcium [Ca] in the blood), kidney damage due to hypercalcemia and calcium deposit in the various tissues. The anti-vitamin of D is PHYTIC acid.
Vitamin E (anti-sterility)
They are fat-soluble vitamins of group E: α-, β-, γ-, δ- tocopherols; derive mainly from vegetable oils, wheat germ, whole grains, eggs, liver, legumes, dried fruit and green leafy vegetables. Tocopherols are powerful antioxidants, protect cell membranes and therefore are anti-tumor. Vitamin E is absorbed with lipids in the small intestine for about 33% of the total ingested with food and is deposited in the liver. Deficiency causes damage to red blood cells, muscular dystrophy and fetal death in pregnant women, while excess causes headache, nausea, fatigue and bleeding.
Vitamina K (antiemorragica)
are fat-soluble of the K group: k1 phylloquinone, K2 farnoquinone and K3 menadione; the food sources are green leafy vegetables but it is also synthesized by the intestinal bacterial flora. It is essential for blood coagulation because it promotes the synthesis of coagulation factors such as pro-thrombin; it is absorbed with fats in the small intestine and any deficiency (sometimes induced by biliary or liver diseases) causes haemorrhage / s. Excess, in newborns, manifests itself with jaundice and anemia, while in adults it causes thrombosis and vomiting. The anti-vitamin of K is CUMARIN.
Vitamins F (essential fatty acids - AGE)
They are fat-soluble of the "F" group: omega6 (linoleic acid, γ-linolenic acid, diomo-γ-linolenic acid and arachidonic acid) and omega3 (α-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid). They can also be considered as vitamin-like factors and are found predominantly in vegetable oils, dried fruit, wheat germ, cold sea fish and oily fish. AGEs hinder the deposition and oxidation of cholesterol in the arteries by promoting the synthesis of HDL and reducing LDL, regulate blood pressure, reduce triglycerides in the blood, are essential constituents of the membrane, precursors of coagulation factors and modulators of the inflammatory state . The absorption of AGEs follows that of lipids in the intestine; the deficiency causes dryness and peeling of the skin while the excess, for omega6, is still the subject of discussions and controversies.
The absorption of fat-soluble vitamins is always favored by the action of bile juices; they are absorbed together with the other lipids and, in the long term, digestive difficulties (lack of endogenous enzymes or absence of the gallbladder) or absorption (see drugs or dietary supplements) can cause their deficiency. They are all sensitive to heat, light and oxygen, except for vitamin D which resists up to 125 ° C; the intake of vitamin K is significantly reduced by antibiotics.
NB. Vitamin K is almost absent in the newborn (as it has no intestinal flora) which often requires an anti-haemorrhagic injection, but WARNING! Excessive dosage can lead to side effects (see above: Vitamin K excess in infants).