B vitamins are a class of water-soluble that play important roles in cell metabolism and synthesis of red blood cells. They are a diverse class of compounds.
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, while some are more commonly recognized by name than by number, such as pantothenic acid (B5), biotin (B7), and folate (B9). B vitamins are present in protein-rich foods, such as fish, poultry, meat, , and eggs; they are also found in Leaf vegetable, , and . Fortified foods, such as , baked products, and , may contain B vitamins.
Each B vitamin is either a cofactor (generally a coenzyme) for key metabolism processes or is a precursor needed to make one.
+ List of B vitamins ! scope="col" data-sort-type="number" | Vitamin ! scope="col" | Name ! scope="col" | Description |
Niacinamide | |||
Nicotinamide riboside | |||
Pyridoxal | |||
Pyridoxamine | |||
Note: Other substances once thought to be vitamins were given B-numbers, but were disqualified once discovered to be either manufactured by the body or not essential for life. See #Related compounds for numbers Choline, Inositol, 10, 11, and others.
Sources for B vitamins also include spinach, (pulses or beans), whole grains, asparagus, potatoes, bananas, chili peppers, . 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 , 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.
To the right, a diagram of some of the major B vitamins (2, 3, 5, 9, and 12) are shown as precursors for certain essential biochemical reactants (FAD, NAD+, coenzyme A, and heme B respectively). The structural similarities between them are highlighted, which illustrates the precursor nature of many B vitamins while also showing the functionality of the end product used by essential reactions to support human, animal, or cellular life.
FAD, NAD+, and coenzyme A are all essential for the catabolic release of free energy (dG) to power the activity of the cell and more complex life forms. See the article on Catabolism for more details on how these three essential biochemical reactants help support life.
Tetrahydrofolate is a necessary co-reactant for synthesizing some amino acids, such as glycine. Heme B is the porphyrin derivative macrocycle molecule that holds the iron atom in place in hemoglobin, allowing for the transportation of oxygen through blood.
! Vitamin B1 | Thiamine | Thiamine deficiency causes beriberi. Symptoms of this disease of the nervous system include weight loss, emotional disturbances, Wernicke encephalopathy (impaired sensory perception), weakness and pain in the limbs, periods of Heart arrhythmia, and edema (swelling of bodily tissues). Heart failure and death may occur in advanced cases. Chronic thiamine deficiency can also cause alcoholic Korsakoff syndrome, an irreversible dementia characterized by amnesia and compensatory confabulation. |
! Vitamin B2 | Riboflavin | Riboflavin deficiency can cause ariboflavinosis, which may result in cheilosis (cracks in the lips), high sensitivity to sunlight, angular cheilitis, glossitis (inflammation of the tongue), seborrheic dermatitis or pseudo-syphilis (particularly affecting the scrotum or labia majora and the nasolabial folds), sore throat (sore throat), hyperemia, and edema of the Pharynx and mucous membrane. |
! Vitamin B3 | Niacin | Niacin deficiency, along with a deficiency of tryptophan, causes pellagra. Symptoms include aggression, dermatitis, insomnia, weakness, mental confusion, and diarrhea. In advanced cases, pellagra may lead to dementia and death (the 3(+1) D's: dermatitis, diarrhea, dementia, and death). |
! Vitamin B5 | Pantothenic acid | Pantothenic acid deficiency can result in acne and paresthesia, although it is uncommon. |
! Vitamin B6 | Pyridoxine, pyridoxal, pyridoxamine | Vitamin B6 deficiency causes seborrhoeic dermatitis-like eruptions, pink eye and neurological symptoms (e.g. epilepsy). |
! Vitamin B7 | Biotin | Biotin deficiency does not typically cause symptoms in adults, other than cosmetic issues such as decreased hair and nail growth, but may lead to impaired growth and neurological disorders in infants. Multiple carboxylase deficiency, an inborn error of metabolism, can lead to biotin deficiency even when dietary biotin intake is normal. |
! Folate | Folic acid | Folic acid deficiency results in a macrocytic anemia, and elevated levels of homocysteine. Deficiency in pregnant women can lead to birth defects, particularly neural tube defects such as spina bifida and anencephaly. |
!Vitamin B12 | | Vitamin B12 deficiency results in a macrocytic anemia, elevated methylmalonic acid and homocysteine, peripheral neuropathy, sense loss, change in mobility, memory loss and other cognitive deficits. It is most likely to occur among elderly people, as absorption through the gut declines with age; the autoimmune disease pernicious anemia is another common cause. It can also cause symptoms of mania and psychosis. Untreated, it is possible to cause irreversible damage to the brain and nerve system — In rare extreme cases, paralysis can result. |
! Vitamin B1 | None | No known toxicity from oral intake. There are some reports of anaphylaxis caused by high-dose thiamin injections into the vein or muscle. However, the doses were greater than the quantity humans can physically absorb from oral intake. |
! Vitamin B2 | None | No evidence of toxicity based on limited human and animal studies. The only evidence of adverse effects associated with riboflavin comes from in vitro studies showing the production of reactive oxygen species (free radicals) when riboflavin was exposed to intense visible and UV light. |
!Vitamin B3 | US UL = 35 mg as a dietary supplement | Intake of 3000 mg/day of nicotinamide and 1500 mg/day of nicotinic acid are associated with nausea, vomiting, and signs and symptoms of liver toxicity. Other effects may include glucose intolerance, and (reversible) ocular effects. Additionally, the nicotinic acid form may cause vasodilatory effects, also known as flushing, including redness of the skin, often accompanied by an itching, tingling, or mild burning sensation, which is also often accompanied by pruritus, headaches, and increased intracranial blood flow, and occasionally accompanied by pain. Medical practitioners prescribe recommended doses up to 2000 mg per day of niacin in either immediate-release or slow-release formats, to lower plasma triglycerides and low-density lipiprotein cholesterol. |
! Vitamin B5 | None | No toxicity known. |
! Vitamin B6 | US UL = 100 mg/day; EU UL = 25 mg/day | See Megavitamin-B6 syndrome for more information. |
! Vitamin B7 | None | No toxicity known. |
! Folate | 1 mg/day | Masks B12 deficiency, which can lead to permanent neurological damage. |
! Vitamin B12 | None established | Skin and spinal lesions. Acne-like rash (causality is not conclusively established). |
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