b vitamins b vitamins b vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells. though these vitamins share similar names (b1, b2, b3, etc.), they are chemically distinct compounds 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 number or name of each vitamin, such as b1 for thiamine, b2 for riboflavin, and b3 for niacin. some are more commonly recognized by name than by number, for example pantothenic acid, biotin, and folate. each b vitamin is either a cofactor (generally a coenzyme) for key metabolic processes or is a precursor needed to make one. list of b vitamins list of b vitamins vitamin name description vitamin b1 thiamine a coenzyme in the catabolism of sugars and amino acids. vitamin b2 riboflavin a precursor of coenzymes called fad and fmn, which are needed for flavoprotein enzyme reactions, including activation of other vitamins vitamin b3 niacin (nicotinic acid) a precursor of coenzymes called nad and nadp, which are needed in many metabolic processes. nicotinamide nicotinamide riboside vitamin b5 pantothenic acid a precursor of coenzyme a and therefore needed to metabolize many molecules. vitamin b6 pyridoxine a coenzyme in many enzymatic reactions in metabolism. pyridoxal pyridoxamine vitamin b7 biotin a coenzyme for carboxylase enzymes, needed for synthesis of fatty acids and in gluconeogenesis. vitamin b9 folate a precursor needed to make, repair, and methylate dna; a cofactor in various reactions; especially important in aiding rapid cell division and growth, such as in infancy and pregnancy. vitamin b12 cobalamins commonly cyanocobalamin or methylcobalamin in vitamin supplements. a coenzyme involved in the metabolism of every cell of the human body, especially affecting dna synthesis and regulation, but also fatty acid metabolism and amino acid metabolism. note: other substances once thought to be vitamins were given numbers in the b-vitamin numbering scheme, but were subsequently discovered to be either manufactured by the body or not essential for life, thus not meeting the two essential qualifiers for a vitamin. see section #related compounds for numbers 4, 8, 10, 11, and others. sources b vitamins are found in abundance in meat, eggs, and dairy products. processed carbohydrates such as sugar and white flour tend to have lower b vitamin 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. sources for b vitamins also include spinach, legumes (pulses or beans), whole grains, asparagus, potatoes, bananas, chili peppers, breakfast cereals. the b12 vitamin is not abundantly available from plant products (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), 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. 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. because they are soluble in water, excess b vitamins are generally readily excreted, although individual absorption, use and metabolism may vary. 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. 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. molecular functions vitamin name structure molecular function vitamin b1 thiamine thiamine plays a central role in the release of energy from carbohydrates. it is involved in rna and dna production, as well as nerve function. its active form is a coenzyme called thiamine pyrophosphate (tpp), which takes part in the conversion of pyruvate to acetyl coenzyme a in metabolism. vitamin b2 riboflavin riboflavin is involved in release of energy in the electron transport chain, the citric acid cycle, as well as the catabolism of fatty acids (beta oxidation). vitamin b3 niacin niacin is composed of two structures: nicotinic acid and nicotinamide. there are two co-enzyme forms of niacin: nicotinamide adenine dinucleotide (nad) and nicotinamide adenine dinucleotide phosphate (nadp). both play an important role in energy transfer reactions in the metabolism of glucose, fat and alcohol. nad carries hydrogens and their electrons during metabolic reactions, including the pathway from the citric acid cycle to the electron transport chain. nadp is a coenzyme in lipid and nucleic acid synthesis. vitamin b5 pantothenic acid pantothenic acid is involved in the oxidation of fatty acids and carbohydrates. coenzyme a, which can be synthesised from pantothenic acid, is involved in the synthesis of amino acids, fatty acids, ketone bodies, cholesterol, phospholipids, steroid hormones, neurotransmitters (such as acetylcholine), and antibodies. vitamin b6 pyridoxine, pyridoxal, pyridoxamine the active form pyridoxal 5'-phosphate (plp) (depicted) serves as a cofactor in many enzyme reactions mainly in amino acid metabolism including biosynthesis of neurotransmitters. vitamin b7 biotin biotin plays a key role in the metabolism of lipids, proteins and carbohydrates. it is a critical co-enzyme of four carboxylases: acetyl coa carboxylase, which is involved in the synthesis of fatty acids from acetate; pyruvate coa carboxylase, involved in gluconeogenesis; β-methylcrotonyl coa carboxylase, involved in the metabolism of leucine; and propionyl coa carboxylase, which is involved in the metabolism of energy, amino acids and cholesterol. vitamin b9 folate folate acts as a co-enzyme in the form of tetrahydrofolate (thf), which is involved in the transfer of single-carbon units in the metabolism of nucleic acids and amino acids. thf is involved in purine and pyrimidine nucleotide synthesis, so is needed for normal cell division, especially during pregnancy and infancy, which are times of rapid growth. folate also aids in erythropoiesis, the production of red blood cells. vitamin b12 cobalamin vitamin b12 is involved in the cellular metabolism of carbohydrates, proteins and lipids. it is essential in the production of blood cells in bone marrow, and for nerve sheaths and proteins. vitamin b12 functions as a co-enzyme in intermediary metabolism for the methionine synthase reaction with methylcobalamin, and the methylmalonyl coa mutase reaction with adenosylcobalamin. deficiencies