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.
| Vitamin | Name | Deficiency effects |
| Vitamin B1 | thiamine | Deficiency causes beriberi. Symptoms of this disease of the nervous system include weight loss, emotional disturbances, Wernicke's encephalopathy (impaired sensory perception), weakness and pain in the limbs, periods of irregular heartbeat, and edema (swelling of bodily tissues). Heart failure and death may occur in advanced cases. Chronic thiamine deficiency can also cause Korsakoff's syndrome, an irreversible psychosis characterized by amnesia and confabulation. |
| Vitamin B2 | riboflavin | Deficiency causes ariboflavinosis. Symptoms may include 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 mouth), pharyngitis, hyperemia, and edema of the pharyngeal and oral mucosa. |
| Vitamin B3 | 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. |
| Vitamin B5 | pantothenic acid | Deficiency can result in acne and paresthesia, although it is uncommon. |
| Vitamin B6 | pyridoxine | Deficiency may lead to anemia, depression, dermatitis, high blood pressure (hypertension), water retention, and elevated levels of homocysteine. |
| Vitamin B7 | biotin | Deficiency does not typically cause symptoms in adults but may lead to impaired growth and neurological disorders in infants. |
| Vitamin B9 | folic acid | Deficiency results in a macrocytic anemia, and elevated levels of homocysteine. Deficiency in pregnant women can lead to birth defects. Supplementation is often recommended during pregnancy. Researchers have shown that folic acid might also slow the insidious effects of age on the brain. |
| Vitamin B12 | cobalamin | Deficiency causes macrocytic anemia, elevated homocysteine, peripheral neuropathy, 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. In rare extreme cases, paralysis can result. |
Note: B16, B17, B18, B19, B20, B21 & B22 do not appear to be animal factors but are claimed by some naturopaths as human therapedic factors.
The B vitamins often work together to deliver a number of health benefits to the body. B vitamins have been shown to:
Together, they also help combat the symptoms and causes of stress, depression, and cardiovascular disease.
All B vitamins are water soluble, and are dispersed throughout the body. Most of the B vitamins must be replenished daily, since any excess is excreted in the urine. A six year cobalamin store can be found in the liver, despite its water soluble nature.
Different B vitamins come from different natural sources, such as potatoes, bananas, lentils, chile peppers, tempeh, liver oil, liver, turkey, tuna, Nutritional yeast (or brewer's yeast) and molasses. Marmite and Vegemite bill themselves as "one of the world's richest known sources of vitamin B". As might be expected, due to its high content of brewer's yeast, beer is a source of B vitamins, although this may be less true for filtered beersand the alcohol in beer impairs the body's ability to activate vitamins.
The B-12 vitamin is of note because it is not available from plant products, making B-12 deficiency a concern for vegans. Manufacturers of plant-based foods will sometimes report B-12 content, leading to confusion about what sources yield B-12. The confusion arises because the standard US Pharmacopeia (USP) method for measuring the B-12 content does not measure the B-12 directly. Instead, it measures a bacterial response to the food. Chemical variants of the B-12 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 B-12 content in other types of foods as well.
Vitamin B may also be delivered by injection to reverse deficiencies.
Another popular means of increasing one's vitamin B intake is through the use of dietary supplements purchased at supermarkets, health centers, or natural food stores. B vitamins are also commonly added to energy drinks. Many energy drinks have been marketed with large amounts of B vitamins ("5-Hour Energy contains an astounding 8,333% of the recommended dietary allowance of vitamin B-12 and 2,000% of the RDA for vitamin B-6.… Red Bull…offers 360% of the RDA for vitamin B-6, 120% of B12, 140% of niacin (vitamin B3)") with claims that this will cause the consumer to "sail through your day without feeling jittery or tense." Nutritionists, such as Professor Hope Barkoukis, dismiss these claims "It's brilliant marketing, but it doesn't have any basis [in fact]." While B vitamins do "help unlock the energy in foods…Just about everyone in America already gets all of the B vitamins they could possibly need in their diets…Extra B vitamins are generally just flushed out of the system." While the elderly may need to supplement their intake of B-12 and other B vitamins due to problems in absorption, "for typical consumers of energy supplements or drinks, B vitamins are nothing more than a 'gimmick'."