Generality
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 .
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 causes hypervitaminosis (toxic state due to usually pharmacological overdoses).
Classification by solubility
Vitamins can be identified by nomenclature, with a letter of the alphabet or with reference to chemical characteristics or biological activities. The most common classification refers 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).
- Fat-soluble vitamins (soluble in fats): vitamin A, vitamin D, vitamin E, vitamin K, vitamin "F" or essential fatty acids (AGE).
Fat-soluble vitamins
The fat-soluble vitamins are A, D, E, K and "F". Let's look at them in detail:
- Vitamin A ( antixeroftalmica ): they are liposoluble vitamins of group A: vitamin A1 (retinol), vitamin A2 (3-deidroretinol) and provitamins (-carotenes). In the animal tissues the A1 and A2 are found (also called retinol 1 and 2), while in vegetables the provitamins are diffused subsequently converted in the animals to hepatic level. Food sources are yolk, liver, milk and derivatives, butter, yellow and orange or green colored vegetables. The liposoluble type A vitamins are used 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 along with the lipids and are stored in the liver. The deficiency causes night blindness, corneal compromise (xerophthalmia), reduced growth, tooth rupture and predisposition to tumors. Excess causes: irritability, nausea, vomiting, growth retardation, liver damage, baldness, fetal malformation and other symptoms.
- Vitamin D ( antirachitica ): they are liposoluble vitamins of group D: vitamin D2 (ergocalciferol) and vitamin D3 (colecalciferol). The ergocalciferol is obtained from ergosterol, a molecule of vegetable origin, while the cholecalciferol is of animal origin. At endogenous level, the synthesis precursor of colecalciferol is 7-dehydrocholesterol, subsequently transformed at the skin level by irradiation of ultraviolet rays (UV). Cholecalciferol is found in milk, yolk, tuna, salmon and cod liver oil. The liposoluble vitamins of group D intervene in the regulation of phosphorus (P) and are essential for ossification; most of the portion ingested with food is NOT used (about 70%) while the most important source is always endogenous synthesis in the skin. Vitamin D deficiency in children causes rickets, in adults osteomalacia and probably also osteoporosis in the elderly. Excess causes nausea, weight loss, irritability, growth retardation, hypercalcemia (calcium [Ca] in the blood), kidney damage due to hypercalcaemia and calcium deposits in various tissues. The anti-vitamin of D is the PHYTIC acid.
- Vitamin E ( anti-sterility ): they are liposoluble vitamins of the E group: α-, β-, γ-, δ-tocopherols; they derive mainly from vegetable oils, wheat germ, whole grains, eggs, liver, legumes, dried fruit and green leafy vegetables. Tocopherols are powerful antioxidants, they protect cell membranes and are therefore 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. The deficiency causes damage to red blood cells, muscular dystrophy and death of the fetus in pregnant women, while excess results in headache, nausea, fatigue and bleeding.
- Vitamin K ( anti-haemorrhagic ): they are liposoluble in the K group: k1 phylloquinone, K2 farnochinone and K3 menadione; dietary sources are green leafy vegetables but are also synthesized by 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 bile or liver problems) causes hemorrhage / e. Excess in newborns is manifested by jaundice and anemia, while in adults it causes thrombosis and vomiting. The K anivitamin is CUMARINA.
- Vitamins F (essential fatty acids - AGE): they are liposoluble in the "F" group: omega6 (linoleic acid, γ-linolenic acid, diomo-γ-linolenic acid and arachidonic acid) and omega3 (α-linolenic acid, eicosapentaenoic acid and acid) docosahexaenoic). They can also be considered vitamino-like factors and are found mainly in vegetable oils, in dried fruit, in wheat germ, in cold-sea fish and in blue fish. AGEs prevent the deposition and oxidation of cholesterol in the arteries by promoting HDL synthesis and reducing LDL, regulating blood pressure, reducing triglycerides in the blood, 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 leads to dryness and peeling of the skin while the excess, for the omega6, is still the subject of discussion and controversy.
The absorption of fat-soluble vitamins is always favored by the action of bile juices; they are absorbed along with the other lipids and, in the long term, a digestive difficulty (lack of endogenous enzymes or absence of the gallbladder) or absorption (see drugs or dietary supplements) can cause the 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 bacterial flora) which often requires an anti-haemorrhagic injection, but ATTENTION! Overdosing can lead to side effects (see above: excess vitamin K in newborns).
