Skoči na - Скочи на: , Grupu jedinjenja, koju jednim imenom nazivamo kompleks ili grupa vitamina B, čine jedinjenja koja su među najneophodnijim za normalno funkcionisanje organizama, usled uloge u kritičnim reakcijama metabolizma. U grupu vitamina B spadaju: vitamin B1, vitamin B2, vitamin B3, vitamin B5, vitamin B6, vitamin B9, vitamin B12. Ranije se smatralo da je vitamin B jedna posebna materija, ali se danas zna da on u stvari predstavlja kompleks odnosno smesu vitamina koji se uglavnom javljaju zajedno, u istim namirnicama. Kvasac, crni hleb i sveže meso, naročito jetra, predstavljaju bogate izvore vitamina B. Najvažniji vitamini B – kompleksa su: B1, niacin, B2, B6, folna kiselina, B12, biotin i pantotenska kiselina. Vitamin B1 (tiamin) se nalazi u ljuskama žitarica, kvascu, jetri, mleku i povrću, ali je osetljiv na toplotu i uništava se kuvanjem. Uloga ovog vitamina je da učestvuje u metabolizmu šećera, a njegov nedostatak izaziva oboljenje beri-beri, koje dovodi do oštećenja nervnog tkiva i poremećaja srčanog rada.
Ljuske pirinča sadrže tiamin, pa se beri-beri javlja u zemljama u kojima oljušteni pirinač predstavlja glavni deo ishrane. Niacin (nikotinska kiselina), takođe, učestvuje u procesima proizvodnje energije u ćelijama. Nedostatak ovog vitamina izaziva oboljenje pelagru koja se ispoljava pojavom proliva, zapaljenja kože, utučenosti i duševnih poremećaja. Meso, naročito jetra, kvasac, neljuštene žitarice, grašak, koštunjavi plodovi, mleko, jaja predstavljaju bogate izvore niacina. Vitamin B2 (riboflafin) se nalazi u mesu, ribi, mleku, siru, belancetu jajeta i lisnatom zelenom povrću. Nedostatak ovog vitamina dovodi do usporavanje rasta i ispucalosti usana (heliozis) i jezika (glositis). Vitamin B6 (piridoksin) je zastupljen u brojnim namirnicama, uključujući meso, neljuštene žitarice, mahune i većinu vrsta povrća. Nedostatak piridoksina se javlja veoma retko i dovodi do malokrvosti i mišićevih grčeva kod dece. Folna kiselina ima važnu ulogu u sintezi DNK koja izgrađuje gene u ćeliji.
Naziv „folna“ potiče od latinske reči „folium“ što znači list, i lisnato zeleno povrće npr. spanać, predstavlja osnovni izvor ovog vitamina. Nedostatak folne kiseline dovodi do poremećaja u ćelijskoj deobi pa je, zbog toga, ona od izuzetnog značaja u periodu rasta i trudnoći, a u odraslih osoba može da izazove malokrvnost. Trudnicama se često prepisuju dodatne količine folne kiseline i vitamina B12. Vitamin B12 (cijankobalamin) se nalazi u mesu, mleku i jajima, ali nije zastupljen u povrću. Osobe koje se strogo pridržavaju vegeterijanske ishrane, mogu usled nedostatka ovog vitamina da pate od malokrvnosti koja je slična pernicioznoj amneziji, pa im se preporučuje da uzimaju dodatne količine ovog vitamina. Biotin i pantotenska kiselina takođe pripadaju vitaminima B kompleksa i potrebni su ljudskom organizmu, ali je njihov nedostatak izuzetno retka pojava. Izvor: Zdrav Život , Zdravlje Nedovršeni članak Vitamin B koji govori o biologiji je u začetku.
Vitamin B na Wikimedijinoj ostavi B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism. Though these vitamins share similar names, research shows that they are chemically distinct vitamins that often coexist in the same foods. In general, dietary supplements containing all eight are referred to as a vitamin B complex. Individual B vitamin supplements are referred to by the specific name of each vitamin (e.g. B1, B2, B3 etc.). Each B vitamin is either a cofactor (generally a coenzyme) for key metabolic processes or is a precursor needed to make one. Note: other substances once thought to be vitamins were given numbers in the B-vitamin numbering scheme, but were subsequently discovered to be either not essential for life or manufactured by the body, thus not meeting the two essential qualifiers for a vitamin. That is why those numbers (4, 8, 10, 11) no longer appear in the classification. Several named vitamin deficiency diseases may result from the lack of sufficient B vitamins.
Deficiencies of other B vitamins result in symptoms that are not part of a named deficiency disease. Because water-soluble B vitamins are eliminated in the urine, taking large doses of certain B vitamins usually only produces transient side-effects. General side effects may include restlessness, nausea and insomnia. These side-effects are almost always caused by dietary supplements and not foodstuffs. B vitamins are found in whole unprocessed foods. Processed carbohydrates such as sugar and white flour tend to have lower B vitamin than their unprocessed counterparts. For this reason, it is required by law in many countries (including the United States) that the B vitamins thiamine, riboflavin, niacin, and folic acid be added back to white flour after processing. This is sometimes called "Enriched Flour" on food labels. B vitamins are particularly concentrated in meat such as turkey, tuna and liver.[18] Good sources for B vitamins include legumes (pulses or beans), whole grains, potatoes, bananas, chili peppers, tempeh, nutritional yeast, brewer's yeast, and molasses.
Although the yeast used to make beer results in beers being a source of B vitamins,[19] their bioavailability ranges from poor to negative as drinking ethanol inhibits absorption of thiamine (B1),[20][21] riboflavin (B2),[22] niacin (B3),[23] biotin (B7),[24] and folic acid (B9).[26] In addition, each of the preceding studies further emphasizes that elevated consumption of beer and other alcoholic beverages results in a net deficit of those B vitamins and the health risks associated with such deficiencies. The B12 vitamin is of note because it is not available from plant products, making B12 deficiency a legitimate concern for vegans. Manufacturers of plant-based foods will sometimes report B12 content, leading to confusion about what sources yield B12. The confusion arises because the standard US Pharmacopeia (USP) method for measuring the B12 content does not measure the B12 directly. Instead, it measures a bacterial response to the food. Chemical variants of the B12 vitamin found in plant sources are active for bacteria, but cannot be used by the human body.
This same phenomenon can cause significant over-reporting of B12 content in other types of foods as well. Another popular means of increasing one's vitamin B intake is through the use of dietary supplements. B vitamins are also commonly added to energy drinks, many of which have been marketed with large amounts of B vitamins[28] with claims that this will cause the consumer to "sail through your day without feeling jittery or tense."[28] Some nutritionists have been critical of these claims, pointing out for instance that while B vitamins do "help unlock the energy in foods," most Americans acquire the necessary amounts easily in their diets. Because they are soluble in water, excess B vitamins (such as may be ingested via supplements) are generally readily excreted, although individual absorption, use and metabolism may vary…"[28] The elderly and athletes may need to supplement their intake of B12 and other B vitamins due to problems in absorption and increased needs for energy production.
[] In cases of severe deficiency, B vitamins, especially B12, may also be delivered by injection to reverse deficiencies.[] Both type 1 and type 2 diabetics may also be advised to supplement thiamine based on high prevalence of low plasma thiamine concentration and increased thiamine clearance associated with diabetes.[30] Also, Vitamin B9 (folic acid) deficiency in early embryo development has been linked to neural tube defects. Thus, women planning to become pregnant are usually encouraged to increase daily dietary folic acid intake and/or take a supplement. Many of the following substances have been referred to as vitamins as they were once believed to be vitamins. They are no longer considered as such, and the numbers that were assigned to them now form the "gaps" in the true series of B-complex vitamins described above (e.g., there is no vitamin B4). Some of them, though not essential to humans, are essential in the diets of other organisms; others have no known nutritional value and may even be toxic under certain conditions.