The vitamin B complex consists of eight water soluble vitamins. The B vitamins work together to boost metabolism, enhance the immune system and nervous system, keep the skin and muscles healthy, encourage cell growth and division, and other benefits to your body. Brewer's yeast is one of the best sources of the B vitamins.

B1, known as thiamine, serves as a catalyst in carbohydrate metabolism and helps synthesize nerve-regulating substances. Deficiency can cause heart swelling, leg cramps, and muscular weakness. Rich food sources high in thiamine include liver, heart, and kidney meats, eggs, leafy green vegetables, nuts, legumes, berries, wheat germs, and enriched cereals. The Recommended Dietary Allowance (RDA) is 1.5 mg. Some believe thiamine helps protect against alcoholism and that it is good for depression, stress, and anxiety. It is also said to improve mental ability and to help indigestion.

B2, or riboflavin, helps metabolize fats, carbohydrates, and respiratory proteins. A deficiency can result in skin lesions and light sensitivity. Riboflavins are abundant in mushrooms, milk, meat, liver, dark green vegetables, and enriched cereals, pasta, and bread. The vitamin is good for the skin, nails, eyes, mouths, lips, and tongue, and it is believed to help protect against cancer.

B3—also known as niacin, vitamin P, or vitamin PP—helps release energy from nutrients. It can reduce cholesterol and prevent and treat arteriosclerosis, among other benefits. Too little B3 can result in pellagra, a disease with symptoms that include sunburn, diarrhea, irritability, swollen tongue, and mental confusion. Too much B3 can result in liver damage. Food sources rich in niacin are chicken, salmon, tuna, liver, nuts, dried peas, enriched cereals, and dried beans.

B5, or Pantothenic acid, has a role in the metabolism of fats, carbohydrates, and proteins. It is most abundant in eggs, whole grain cereals, legumes, and meat, although it is found in some quantity in nearly every food. Deficiency can result in fatigue, allergies, nausea, and abdominal pain.

Vitamin B6, or pyridoxine, helps the body to absorb and metabolize amino acids, to use fats, and to form red blood cells. Deficiency in the vitamin may result in smooth tongue, skin disorders, dizziness, nausea, anemia, convulsions, and kidney stones. Whole grains, bread, liver, green beans, spinach, avocadoes, and bananas are rich food sources that are high in this vitamin.

B7—also known as Biotin or vitamin H, helps form fatty acids and assists in the release of energy from carbohydrates. There have been no cases of deficiency among humans.

B9, or folic acid, sometimes goes by the name of vitamin M or vitamin B-c. Folic acid enables the body to form hemoglobin. It helps treat anemia and sprue. Good food sources include leafy green vegetables, nuts, whole grains, legumes, and organ meets. However, bear in mind that folic acid is lost when foods are stored at room temperature or cooked. Deficiency is rare, although folic acid is particularly important in pregnancy. Consuming adequate folic acid before and during pregnancy helps prevent neural tube defects in newborns, including spina bifida.

Vitamin B12, also known as Cobalamin or Cyanocobalamin, assists the function of the nervous system and the formation of red blood cells. If the body is unable to absorb sufficient B12, pernicious anemia can result. B12 can only be found in animal sources such as eggs, milk, fish, meat, and liver. Therefore, vegetarians are strongly encouraged to supplement.