B Vitamins Fact Sheet

The B vitamins have a wide and varied range of functions in the human body. Most B vitamins are involved in the process of converting blood sugar into energy. Diets rich in these vitamins are particularly important for pregnant and breast-feeding women and for people who require more energy, such as athletes and heavy-labor workers.

General deficiencies of vitamin B
Deficiencies of B vitamins are uncommon in the US, but when they occur they usually involve several B vitamins because many of them come from the same food groups. Alcohol interferes with the body’s absorption of these vitamins. Elderly people are at risk for vitamin B deficiencies because they often have inadequate diets, and prescribed medications may interfere with B-vitamin absorption.

General toxicity of vitamin B
Because the B vitamins are water soluble and eliminated in the urine, toxic reactions from oral administration of most B vitamins are extremely rare, the exceptions being niacin and B6. (For specific adverse reactions from deficiencies or high dosage levels, see individual discussions of B vitamins, below.) It should be noted that B15 (pangamic acid) and B17 (laetrile) are neither vitamins nor nutrients. These are chemicals that are highly dangerous and have no proven nutritional or other value.

Deficiencies and toxicity of vitamin B1
Thiamin is essential for converting blood sugar into energy and is involved in metabolic activities in the nerves, heart and muscles, and in the production of red blood cells. Thiamin is found in almost all foods, but the best source is pork. Good sources of thiamin include dried fortified cereals, oatmeal, corn, nuts, cauliflower and sunflower seeds. Recommended RDA is 1.2 mg per day for men and 1.1 mg for women. Thiamin supplements for people with normal diets and good health are unnecessary. Severe vitamin B1 deficiency, known as beriberi, is rare in the US but can occur in alcoholics, in severely malnourished people, or in people who receive long-term dialysis or intravenous feeding. Symptoms may include visual disturbances, paralysis, staggering, loss of sensation in the legs and feet, psychosis and congestive heart failure. No toxic effects have been reported for thiamin.

Deficiencies and toxicity of vitamin B2 (riboflavin)
Like thiamin, riboflavin is important in the production of energy. Some dietary sources are liver, dried fortified cereals and low-fat yogurt. The recommended DRI for adults is 1.7 mg. Deficiencies affect the skin and mucous membranes, which may be seen as cracks on the lips or corners of the mouth, eczema of the face and genitals, a burning sensation on the tongue, or eye irritation. Supplements for people with normal diets and health are unnecessary. Large doses of riboflavin are generally considered to have no toxic effects, but one study has indicated that high consumption of vitamin B2 may increase the risk of stomach cancer. (In the same study, vitamins B1, B3 and B6 were protective.)

Deficiencies and toxicity of vitamin B3 (niacin)
Niacin, also known as nicotinic acid, helps break down blood sugar for energy and also acts as a vasodilator, which means it widens blood vessels and increases blood flow. Dietary sources are mackerel, swordfish, chicken, veal, fortified dry cereals, pork, salmon, and beef liver. Current DRI recommendations are 20 mg. Niacin may be prescribed to improve cholesterol levels, but supplements are unnecessary in people with normal health and diets. A deficiency of niacin causes pellagra, a chronic disease that can cause eczema, intestinal and stomach distress, depression, headache, thinning of the hair and excess saliva production. Anemia may occur, although this is probably due to an accompanying deficiency in folic acid. Even mildly high doses of niacin can cause hot flushing of the face and shoulders, headache, itchiness and stomach problems. Some individuals have reported heart disturbances and temporarily lowered blood pressure. Large doses may produce ulcers, gout, diabetes and liver damage, which are usually reversed when high doses are discontinued.

Deficiencies and toxicity of vitamin B5
Pantothenic acid, as with many B vitamins, is involved in metabolism of fats, carbohydrates and proteins, as well as in production of steroid hormones and other important chemicals. Dietary sources are whole grains, beans, milk, eggs and liver. Recommended adequate intake (AI) is 4 to 7 mg. Supplements are unnecessary in people with normal health and diets. Deficiency is unlikely unless there are also other B-vitamin deficiencies. Symptoms of B5 deficiency include abdominal distress, a burning sensation in the heels, and sleep problems. Although no toxicity has been reported in humans, high doses have caused liver damage in rats.

Deficiencies and toxicity of vitamin B6
Vitamin B6, or pyridoxine, affects over 60 proteins in the body; most importantly, those that play a role in the nervous system, in red and white blood cell production and in heart disease. Food sources of B6 are meats, oily fish, poultry, whole grains, fortified dry cereals, soybeans, avocados, baked potatoes with skins, watermelon, plantains, bananas, peanuts and brewer’s yeast. Current DRI recommendations are 2 mg in all adults, although for heart protection some experts recommend 3 to 6 mg. Deficiencies are very uncommon but can cause skin problems and nervous system disorders, including impaired memory and concentration. B6 deficiency may also increase risk of kidney stones. In rare cases, infants are born unable to metabolize. In such cases seizures or convulsions can occur, and vitamin B6 must be administered. Deficiency is associated with increased levels of the chemical homocysteine, which has been associated with heart disease, birth defects and possibly Alzheimer’s disease and dementia. A diet rich in fruits and vegetables may reduce homocysteine levels. Very high doses (2000 mg per day) can cause nerve damage with symptoms of instability and numbness in the feet and hands, which may be permanent in some cases. An excess of B6 also reduces the effects of L-dopa, the drug used to treat Parkinson’s disease.

Deficiencies and toxicity of vitamin B12
Vitamin B12 is essential for the production of blood cells, manufacturing genetic material and for healthy functioning of the nervous system. The only natural dietary sources of B12 are animal products, meats, dairy products, eggs and fish (clams and oily fish are very high in B12), but as with other B vitamins, B12 is added to commercial dry cereals. The RDA is 2.4 mcg a day. Deficiencies are rare in young people, although the elderly may have trouble absorbing natural vitamin B12 and may require synthetic forms from supplements and fortified foods. Symptoms of mild vitamin B12 deficiency include memory loss, instability, disorientation, decreased reflexes and possibly hearing loss. Deficiencies also elevate homocysteine (see Vitamin B6, above). When vitamin B12 deficiencies are due to lack of a protein known as gastric intrinsic factor (a genetic defect), pernicious anemia can develop. This serious disorder must be treated with injections of vitamin B12 to avoid neurologic damage.