B vitamins
B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells.[1][2] They are a chemically diverse class of compounds.[1]
"B complex" redirects here. For the musician, see B-Complex.
Dietary supplements containing all eight are referred to as a vitamin B complex. Individual B vitamins are referred to by B-number or by chemical name, such as B1 for thiamine, B2 for riboflavin, and B3 for niacin,[1][2] while some are more commonly recognized by name than by number, such as pantothenic acid (B5), biotin (B7), and folate (B9).[1] B vitamins are present in protein-rich foods, such as fish, poultry, meat, dairy products, and eggs; they are also found in leafy green vegetables, beans, and peas.[1] Fortified foods, such as breakfast cereals, baked products, and infant formulas, may contain B vitamins.[1]
Each B vitamin is either a cofactor (generally a coenzyme) for key metabolic processes or is a precursor needed to make one.[1][2]
Sources[edit]
B vitamins are found in abundance in meat, eggs, and dairy products.[2] Processed carbohydrates such as sugar and white flour tend to have lower B vitamin content than their unprocessed counterparts. For this reason, it is common in many countries (including the United States) that the B vitamins thiamine, riboflavin, niacin, and folic acid are added back to white flour after processing. This is referred to as "enriched flour" on food labels. B vitamins are particularly concentrated in meat such as turkey, tuna and liver.[3]
Sources for B vitamins also include spinach, legumes (pulses or beans), whole grains, asparagus, potatoes, bananas, chili peppers, breakfast cereals.[2]
The B12 vitamin is not abundantly available from plant products[4] (although it has been found in moderate abundance in fermented vegetable products, certain seaweeds, and in certain mushrooms, with the bioavailability of the vitamin in these cases remaining uncertain),[5] making B12 deficiency a legitimate concern for those maintaining a vegan diet. 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.[6]
A common way to increase vitamin B intake is by using dietary supplements. B vitamins are commonly added to energy drinks, many of which have been marketed with large amounts of B vitamins.[7]
Because they are soluble in water, excess B vitamins are generally readily excreted, although individual absorption, use and metabolism may vary.[7] 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.[8] 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.[9] Also, folate 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 folate intake or take a supplement.[10]
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 (for example, 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.