The Role Of B Vitamins Water-soluble vitamins were collectively called water soluble B in the beginning. When more water-soluble vitamins were discovered, they were referred to as B1, B2, B6, B12 and so on. Later when more vitamins were discovered in both the categories, they were referred as vitamins C, D, E and K. Now, most are known by a word that indicates either chemical nature or function. Some vitamins are synthesized in the body itself by intestinal micro-organisms. Antibiotics and sulfa drugs may destroy these organisms resulting in decreased vitamin synthesis.
There are other bacteria which when present in the intestine utilize dietary vitamins for their own use thus causing vitamin deficiency. Vitamins in the diet are bound to protein and fat. During digestion, they get broken down and absorbed. Vitamins present in undigested food are not available to the body. The body requirement of vitamins depends upon several factors. Apart from those mentioned above, people suffering from tuberculosis or high fever require more vitamins and people living in high altitudes and cold regions also have increased vitamin requirement. 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 B vitamins are particularly important for pregnant and breast-feeding women and for other 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 U.S., but when they occur, they usually involve several B vitamins, since many of them come from the same food groups. Alcohol interferes with these vitamins, and some of the physical and mental problems that alcoholics experience may be attributed to a deficiency of B vitamins. Elderly people are also at risk for deficiencies, because of inadequate diets and potential interference with B-vitamin absorption by medications. General Toxicity of Vitamin B Because the B vitamins are water-soluble and eliminated in the urine, toxic reactions from oral administration of most of them are extremely rare.
(Exceptions are 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 substances known as B15 (pangamic acid) and B17 (laetrile) are neither vitamins nor nutrients; both chemicals are highly dangerous and have no proven nutritional or other value. Deficiencies and Toxicity of Vitamin B1 (Thiamin) Thiamin is essential for converting blood sugar into energy and is involved in metabolic activities in 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 and good sources are 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. Supplements for people with normal diets and health are unnecessary.
Severe vitamin B1 deficiency, known as beriberi, is rare in the U.S., but can occur in alcoholics, in severely malnourished people, or in those receiving 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.
Recommended DRI is 1.7 mg. Supplements for people with normal diets and health are unnecessary. Deficiencies affect the skin and mucous membranes and can cause cracks on the lips or corners of the mouth, eczema of the face and genitals, a burning sensation on the tongue, or eye irritation. Previously, no toxic effects had been reported even from large doses of riboflavin However, one new study 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, widening blood vessels and increasing blood flow. Dietary sources are mackerel, swordfish, chicken, veal, dried fortified cereals, pork, salmon, and beef liver. Current DRI recommendations are 20 mg. This vitamin may be prescribed for improving cholesterol levels, but supplements are unnecessary in people with normal health and diets. A deficiency of niacin causes pellagra; symptoms can include 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 (see Folic Acid, below). Even mildly high doses of niacin can cause hot flushing of the face and shoulders, headache, itchiness, and stomach problems.
Some report 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) Pantothenic acid, like many B vitamins, plays a wide role in the body, including metabolism of fats, carbohydrates, and proteins, as well as 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 except in company with other B vitamin deficiencies. Symptoms include abdominal distress, burning sensation in the heels, and sleep problems. Although no toxicity has been reported in humans, high dosages have caused liver damage in rats. Deficiencies and Toxicity of Vitamin B6 (Pyridoxine) Vitamin B6, or pyridoxine, has an effect on over 60 proteins in the body, 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, dried fortified 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. They may also increase the risk for kidney stones. In rare cases, infants are born unable to metabolize pyridoxine; 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 is turn has been associated with heart disease, birth defects, and possibly Alzheimer’s disease and dementia. (It is not known if reducing homocysteine levels will have any protective effect.) A diet rich in fruits and vegetables may reduce homocysteine levels. Very high doses (2,000 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.
In some cases, the damage may be permanent. Pyridoxine also reduces the effects of L-dopa, the drug used for Parkinson’s disease. Deficiencies and Toxicity of Vitamin B12 (Cobalamin) 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); like other B vitamins, however, B12 is added to commercial dried 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 require synthetic forms from supplements and fortified foods.
Symptoms of mild B12 deficiency include memory loss, instability, disorientation, and decreased reflexes, and possibly and hearing loss. Deficiencies also elevate homocysteine (see vitamin B6, above). When vitamin B12 deficiencies are caused by a genetic defect, in which a protein known as gastric intrinsic factor is lacking, a serious disorder known as pernicious anemia can develop, which must be treated with injections of vitamin B12 or else neurologic damage may occur. Deficiencies and Toxicity of Biotin Biotin, also a B vitamin, is involved in the production of amino acid proteins and fatty acids. It is obtained not only in diet but is also produced by bacteria in the intestines. Dietary sources are eggs, milk, liver, mushrooms, bananas, tomatoes, whole grains, nuts, and brewer’s yeast. There is no DRI for biotin; some experts suggest 30-100 mcg. Deficiencies are almost unheard of.
There is no evidence of toxicity with this vitamin. Deficiencies and Toxicity of Folate Folate is a B vitamin compound that is important for many metabolic processes in the body and is used in the manufacture of neurotransmitters (chemical messengers in the brain), in preventing heart disease, and for synthesizing DNA. Folate is best found in avocado, bananas, orange juice, cold cereal, asparagus, fruits, green, leafy vegetables, dried beans and peas, and yeast. The synthetic form, folic acid, is now added to commercial grain products. Vitamins are usually made from folic acid, which is about twice as potent as folate. Many experts now recommend that adults have 400 mcg of folic acid daily, which is considerably higher than the DRI recommendations of 400 mcg of folate, which does not take into consideration the possible benefits of folate on the heart.
Low levels of folate during pregnancy are common without supplements; deficiencies at that time increase the risk of neural tube defects in newborns. Women who are planning to be pregnant should take 400 mcg of folic acid before conception as well as when they are pregnant or breast feeding. Folate deficiency can cause megaloblastic anemia and affect concentration and memory and may cause hearing loss. As with vitamins B6 and B12, deficiencies also elevate homocysteine, and recent studies are suggesting a strong link between low folate levels and the onset of heart disease. Poor diet coupled with alcoholism is the most common cause of folate deficiency.
Any condition that disturbs the small intestine can contribute to folate deficiency. High-dose aspirin, smoking, treatment for seizures, and oral contraceptives may increase the risk for folate deficiency. Some studies have reported a link between high doses and central nervous system disorders, zinc deficiency, and seizures in epileptics. This risk appears to be low, but these results indicate that megadoses of folic acid should be avoided. High amounts in the elderly may also mask symptoms of vitamin B12 deficiencies. Deficiencies and Toxicity of Choline Choline has recently been recognized as an important B vitamin.
It is particularly essential for fetal brain development and for learning and memory. Peanuts, eggs, cauliflower, and meats, especially liver, are good sources of choline. Recommended daily doses are 425 mg for nonpregnant women, 450 mg for pregnant women, and 550 mg for nursing women. Excessive doses can cause intestinal problems, and there is also some concern that high doses can be carcinogenic. Science.