The primary health benefits of vitamin B lie in getting enough of the vitamin for normal health, and in correcting deficiencies. Increased understanding of the B vitamins has greatly reduced diseases caused by malnutrition. Vitamin B is actually a group of unique, unrelated vitamins that have been linked together since the time early research into vitamins began. Each type of B vitamin may have a therapeutic effect on some health conditions. Supplements containing the "vitamin B complex" are sometimes recommended for a variety of health benefits.
Vitamin B is often called a complex, even though it contains a number of unrelated vitamins. It was once thought to be a single vitamin because most of the B vitamins occur in specific foods, liver being one example. Like vitamin C, all of the B vitamins are water-soluble. For this reason, most of them are quickly passed in urine. One exception is B12, which is stored by the liver, potentially for years.
Thiamine, or vitamin B1, has been studied for possible benefits related to Alzheimer's disease, hepatitis, and patients undergoing frequent dialysis. It also causes rapid improvements in beriberi, a neurological condition caused by B1 deficiency. Vitamin B2 could help relieve migraines, and may have a positive effect on symptoms of Parkinson's disease. Niacin, or vitamin B3, might help lower cholesterol and triglyceride levels in some people. Niacin deficiency is the cause of the disease known as pellagra, a nervous system disorder that is now rare in developed countries.
Vitamin B6 is sometimes deficient in unhealthy Western diets, and could have a positive effect on a number of conditions, including certain types of depression and some skin problems. Vitamin B12, which is necessary for a healthy nervous system, has been studied in relation to numerous health concerns, with positive findings on many fronts. Deficiency of B12 can cause anemia and nervous system disorders. Folic acid, another B vitamin, is especially recommended for women who are pregnant or may become pregnant. Folic acid is also thought to mediate stress responses in the body that can contribute to hypertension and heart disease.
The vitamin B complex is sometimes taken to correct "imbalances" that are thought to occur when a person takes only one specific kind of B vitamin as a supplement. No evidence suggests that such an imbalance can occur. This is because although they are all called B vitamins, they aren't truly related. Alcoholics, who are typically deficient in B vitamins, may benefit from such a supplement.