Pyridoxine, or vitamin B6, is a member of the water-soluble family of B vitamins. It is necessary in the processes to metabolize proteins, fats, and carbohydrates, to make hormones and neurotransmitters, and to support the immune system. It also plays a role in the production of normal, healthy red blood cells and some of the neurotransmitters needed for proper nervous system function. In conjunction with folic acid and cobalamin, it acts to reduce homocysteine levels, thus lowering the risk of developing heart disease .
Mild deficiencies of pyridoxine are common, despite the low daily requirements. The Recommended Daily Allowance (RDA) for babies under six months of age is 0.3 milligrams (mg), and for babies six months to one year old is 0.6 mg. The daily requirement is 1.0 mg for children one to three years old, 1.1 mg for those four to six years old, and 1.4 mg for seven- to ten-year-olds. Males aged 11–14 years need 1.7 mg, and those 15 years and older need 2.0 mg. Women need slightly less; 1.4 mg for females 11–14 years, 1.5 mg for those 15–18 years, and 1.6 mg for women age 19 years and older. Requirements are somewhat increased during pregnancy (2.2 mg) and lactation (2.1 mg).
Pyridoxine has numerous therapeutic uses apart from merely treating deficiency. It has a calming effect on the nervous system, and may alleviate insomnia by increasing serotonin levels in the brain. Because of the calming effects of pyridoxine, it has been tried as a possible adjunctive treatment for schizophrenia . As of 2002, however, the findings are inconclusive. Studies of larger patient populations have been recommended.
There is good evidence that pyridoxine reduces the nausea for about a third of pregnant women who experience morning sickness . In addition, pyridoxine does not have any harmful effects on the fetus. It is also used to decrease the risk of heart disease by lowering homocysteine levels. Taken in conjunction with magnesium supplements, pyridoxine has been found to have beneficial effects on some people with autism . The vitamin B6 and magnesium combination can also help to prevent the recurrence of calcium oxalate kidney stones in susceptible people. Those who are affected by depression or gestational diabetes may benefit from a moderate addition of it, as well. One type of hereditary anemia and several metabolic diseases are effectively treated with high doses of pyridoxine. A few chemotherapeutic agents, including vincristine, can be taken with fewer side effects when pyridoxine is added to the patient's regimen. The data are equivocal on whether or not asthma is improved by vitamin B6 supplementation, but high doses—50 mg, taken twice daily—were used in the studies performed, creating a risk of nerve injury. There is some question as to the benefit to taking it for PMS, carpal tunnel syndrome , or diabetic neuropathy, although there is no harm in a trial of additional B6 at a modest level. Taking B6 has some benefit for those suffering from osteoporosis and epilepsy . Nevertheless, the advice of a health care professional should be sought before undertaking this, and any, supplemental treatment.
Meats are the best food source of pyridoxine, followed by dairy and eggs. Although some grains contain B vitamins, they are generally lost in processing. Bananas, potatoes, mangos, and avocados have the highest vitamin B6 value of the vegetarian foods. Fresh foods should be used, as freezing destroys much of this vitamin. Minimize the amount of water used in cooking, as the pyridoxine and other water soluble vitamins will leach into it.
Pyridoxine supplements are available in both oral and injectable forms. It is also added to many processed grain products. Consider taking a balanced B complex supplement rather than high doses of an individual vitamin unless given medical instructions by a doctor to do so. Store supplements in a cool, dry place, away from light, and out of the reach of children.
Symptoms of pyridoxine deficiency are nonspecific, but may include nervousness, irritability, muscle twitches, insomnia, confusion, weakness, loss of coordination, and anemia. Frequent infections are likely as well due to the importance of vitamin B6 to the immune system.
Risk factors for deficiency
Since meats are the best source of pyridoxine, followed by dairy and eggs, vegans are one of the groups at risk for deficiency. A balanced B vitamin supplement is adequate to prevent deficiency. People with malabsorption syndromes, chronic illnesses, or hyperthyroidism may require somewhat larger amounts of vitamin B6. Those who take birth control pills are more likely to have abnormally low levels, and may benefit from a supplement of 25–50 mg per day. Elderly people are more likely to have a poor diet, and deficient pyridoxine will both increase their susceptibility to illness, and prolong recovery. Alcoholics, smokers, and people who take certain medications including estrogen, theophylline (for asthma), hydralazine (for hypertension ), penicillamine (for rheumatoid arthritis ), and isoniazid (for tuberculosis ) are more likely to need extra pyridoxine. For asthmatics on theophylline, the side effects of this medication can also be reduced by the additional vitamin B6. Consult a health care professional before beginning a program of supplementation.
Allergic reactions to oral or injected pyridoxine are known to occur, but are rare. It is possible to have toxic effects from large doses. At 2,000 mg daily, nerve damage may occur, causing numbness or tingling of the extremities and loss of coordination. These symptoms are usually, but not always, reversible. At 500 mg for daily dosages, there is possible toxicity if chronically taken many months or years. Finally, at 150 mg taken daily, there is rare, but possible, toxicity with long-term use. Thus, it is best to take no more than 50 mg a day unless under medical supervision to avoid the potential for toxicity. Chronic large doses may also cause photosensitivity. Pregnant women who take megadoses may create dependence in the newborn, who would be at risk for seizures. Nursing infants can also suffer adverse effects from large doses ingested in breast milk.
High doses of pyridoxine may cause a rash in addition to the more serious complications listed under precautions.
Optimal levels of riboflavin, vitamin C , magnesium, and selenium improve pyridoxine absorption. The effectiveness of levodopa is reduced by pyridoxine. Anyone taking levodopa, most commonly used to treat Parkinson's disease , should not take supplemental vitamin B6. Other combination forms of medication for Parkinson's disease may not be affected. Phenytoin and phenobarbital, two medications sometimes used to control epilepsy, may also become less effective in the presence of extra vitamin B6. Pyridoxine requirements are increased by the medications hydralazine, penicillamine, isoniazid, and some immunosuppressive agents. Both theophylline and estrogen containing medications, including the birth control pill, block the metabolism of pyridoxine.
Bratman, Steven and David Kroll. Natural Health Bible. Prima Publishing, 1999.
Feinstein, Alice. Prevention's Healing with Vitamins. Pennsylvania: Rodale Press, 1996.
Griffith, H. Winter. Vitamins, Herbs, Minerals & supplements: the complete guide. Arizona: Fisher Books, 1998.
Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's letter/Prescriber's Letter Natural Medicines Comprehensive Database. California: Therapeutic Research Faculty, 1999.
Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. New York: Alpha Books, 1997.
Jewell, D., and G. Young. "Interventions for Nausea and Vomiting in Early Pregnancy." Cochrane Database System Review January 2002: CD000145
Lerner, V., C. Miodownik, A. Kaptsan, et al. "Vitamin B6 as Add-On Treatment in Chronic Schizophrenic and Schizoaffective Patients: A Double-Blind, Placebo-Controlled Study." Journal of Clinical Psychiatry 63 (January 2002): 54-58.
Levichek, Z., G. Atanackovic, D. Oepkes, et al. "Nausea and Vomiting of Pregnancy. Evidence-Based Treatment Algorithm." Canadian Family Physician 48 (February 2002): 267-268, 277.
Rebecca J. Frey, PhD
Vitamin B6 Deficiency
Vitamin B6 Deficiency
Vitamin B6 is used by the body as a catalyst in reactions that involve amino acids. Vitamin B6 deficiency is rare, since most foods eaten contain the vitamin.
Vitamin B6 is a water-soluble vitamin. The recommended dietary allowance (RDA) for vitamin B6 is 2.0 mg/day for the adult man and 1.6 mg/day for the adult woman. Vitamin B6 in the diet generally occurs as a form called pyridoxal phosphate. In this form, it cannot be absorbed by the body. During the process of digestion, the phosphate group is removed, and pyridoxal is produced. However, the body readily absorbs pyridoxal, and converts it back to the active form of the vitamin (pyridoxal phosphate).
Poultry, fish, liver, and eggs are good sources of vitamin B6, comprising about 3-4 mg vitamin/kg food; meat and milk contain lesser amounts of the vitamin. The vitamin also occurs, at about half this level, in a variety of plant foods, including beans, broccoli, cabbage, and peas. Vitamin B6 tends to be destroyed with prolonged cooking, with storage, or with exposure to light.
As mentioned, vitamin B6 takes various forms. One of these forms, called pyridoxine, is relatively stable. For this reason, pyridoxine is the form of vitamin B6 that is used in vitamin supplements, or when foods are fortified. Apples and other fruits are poor sources of the vitamin, containing only 0.2-0.6 mg vitamin/kg food.
Vitamin B6, used mainly in the body for the processing of amino acids, performs this task along with certain enzymes. The enzyme that participates in this type of complex is aminotransferase. Several types of aminotransferase exist. With vitamin B6 deficiency, while aminotransferase continues to occur in the various organs of the body, there is an abnormally low level of the active vitamin B6/aminotransferase complex present. Thus, this vitamin deficiency results in the impairment of a variety of activities in the body. With supplement correction of the vitamin B6 deficiency, the aminotransferase then readily forms the active complex, and normal metabolism is restored.
Vitamin B6 converts certain amino acids (glutamic acid, aspartic acid, glycine) to energy. This allows the body to process all dietary protein, even when the dietary protein is in excess of the body's needs. Vitamin B6 also allows the body to synthesize certain amino acids. For example, if the diet is deficient or low in certain amino acids, such as glycine or serine, vitamin B6 enables the body to make them from sugar. Vitamin B6 is used also for the synthesis of certain hormones, such as adrenaline.
Causes and symptoms
Vitamin B6 deficiency occurs rarely. When it does, it is usually associated with poor absorption of nutrients in the gastrointestinal tract (as in alcoholism, or with chronic diarrhea ), the taking of certain drugs (as isoniazid, hydrolazine, penicillamine) that inactivate the vitamin, with genetic disorders that inhibit metabolism of the vitamin, or in cases of starvation.
The symptoms of vitamin B6 deficiency in adults are only vaguely defined. These include nervousness, irritability, insomnia, muscle weakness, and difficulty in walking. Vitamin B6 deficiency may produce fissures and cracking at the corners of the mouth. The deficiency occurred in infants fed early versions of commercial canned infant formula, when the vitamin had been inadvertently omitted from the formula. This error resulted in infants failing to grow, in irritability, and in seizures.
Vitamin B6 status is measured by the transaminase stimulation test. This test requires extraction of red blood cells, and placement of the cells in two test tubes. Special chemicals (reagents) are added to both test tubes to allow for measurement of aminotransferase. This enzyme requires pyridoxal phosphate. A known quantity of pure pyridoxal phosphate is added to one of the test tubes. The activity level of the enzyme is measured, and compared, in both test tubes. If the added pyridoxal phosphate did not stimulate activity, the patient is considered not to be deficient in vitamin B6. Neither is the patient considered deficient if only slight stimulation occurred. But if a stimulation of four-fold or more occurred, a vitamin B6 deficiency is present.
Vitamin B6 deficiency can be prevented or treated with consumption of the recommended dietary allowance, as supplied by food or by vitamin supplements.
The prognosis for correcting vitamin B6 deficiency is excellent.
Vitamin B6 deficiency is not a major concern for most people. The deficiency can be prevented with consumption of a mixed diet that includes poultry, fish, eggs, meat, vegetables, and grains.
Amino acid— Amino acids are small molecules that are used as building blocks for all proteins. Some amino acids are also used in the body for the manufacture of hormones. There are about 20 nutritionally important amino acids, including glutamic acid, glycine, methionine, lysine, tryptophan, serine, and glycine.
Fat-soluble vitamins— Fat-soluble vitamins can be dissolved in oil or in melted fat.
Recommended Dietary Allowance (RDA)— The Recommended Dietary Allowances (RDAs) are quantities of nutrients in the diet that are required to maintain good health in people. RDAs are established by the Food and Nutrition Board of the National Academy of Sciences, and may be revised every few years. A separate RDA value exists for each nutrient. The RDA values refer to the amount of nutrient expected to maintain good health in people. The actual amounts of each nutrient required to maintain good health in specific individuals differ from person to person.
Water-soluble vitamins— Water-soluble vitamins can be dissolved in water or juice.
Brody, T. Nutritional Biochemistry. San Diego: Academic Press, Inc., 1998.
Pyridoxine (peer-ih-DOCK-seen) is also known as 3-Hydroxy-4,5-bis(hydroxymethyl)-2-methylpyridine; 3-hydroxy-4,5-dimethylol-2-methylpyridine; and vitamin B6. It is a white, odorless, crystalline compound with a slightly bitter taste. The term pyridoxine is also used as a generic term for three compounds with biological activity classified under the term Vitamin B6. The three compounds are pyridoxine, pyridoxal, and pyridoxamine. Pyridoxine is usually produced commercially as the hydrochloride, CH3C5HN(OH)(CH2OH)2·;HCl, which has somewhat different physical characteristics from pyridoxine itself.
Carbon, hydrogen, nitrogen, oxygen
Not applicable; sublimes above melting point
Very soluble in water; slightly soluble in ethyl alcohol and acetone
Vitamin B6 was discovered in 1938 by five groups of researchers working independently. The five groups were all looking for a cure for a disease in rats called acrodynia that resembles the human disease pellagra. In the early 1930s, the Hungarian-American biochemist Albert Szent-Györgi (1893–1986) hypothesized the existence of a vitamin that would cure acryodynia and even gave the vitamin a name, vitamin B6. So the simultaneous discovery of such a compound in 1938 was not much of a surprise.
The first component of vitamin B6, pyridoxine, was first synthesized, also in 1938, by the Austrian-German chemist Richard Kuhn (1900–1967). Its chemical structure was determined a year later by American chemists Karl August Folkers (1906–1997) and S. A. Harris (dates not available) at the Merck chemical corporation. Pyridoxine is the most stable form of the vitamin, so it is the form used in vitamin supplements and as a food additive.
HOW IT IS MADE
Pyridoxine is produced naturally by most plants and animals in sufficient amounts to prevent vitamin B6 deficiency diseases. It is also produced synthetically by a complex series of reactions that begins with isoquinoline (C9H7N).
COMMON USES AND POTENTIAL HAZARDS
Vitamin B6 has been shown to be essential in many biochemical reactions that occur in plants and animals. Although it may occur in any one of the three forms listed above, the compound usually acts as the phosphate ester, pyridoxine phosphate. Pyridoxine phosphate functions as a coenzyme in the transformation of amino acids, the building blocks from which proteins are made. A coenzyme is a chemical compound that works with an enzyme to catalyze some essential chemical reaction in the body. Pyridoxine phosphate appears to be necessary for the synthesis of proteins from amino acids as well as the metabolism of amino acids to produce energy needed for normal body functioning.
Because pyridoxine is water soluble, it dissolves when foods are cooked or processed.
Vitamin B6 deficiency diseases are very rare. In 1954, a batch of commercially prepared baby food was overheated during its preparation. Overheating apparently destroyed the vitamin B6 present in the food. Babies who were fed with the food had convulsions became unusually irritable, and developed unusual behaviors. As soon as the babies were given vitamin B6 supplements, these symptoms disappeared. Such instances among humans are so rare that they become the subject of articles in medical journals. Other reported instances of vitamin B6 deficiency disease have involved pregnant women who did not receive enough of the vitamin in their daily diets and people living in Cuba during the early 1990s who had restricted diets. Symptoms of vitamin B6 deficiency include general weakness, anemia, cracked lips, inflamed tongue and mouth, irritability, depression, and skin disorders.
Meats have the highest concentration of vitamin B6, so vegetarians may be at risk for deficiency disorders. Other foods that contain high concentrations of the vitamin include bananas, mangoes, avocados, and potatoes. Increased doses of vitamin B6 are sometimes used to treat morning sickness and insomnia, and some authorities recommend the vitamin to decrease the risk of heart disease. The maximum recommended dose of vitamin B6 is 50 milligrams a day.
Words to Know
- A material that increases the rate of a chemical reaction without undergoing any change in its own chemical structure.
- The process including all of the chemical reactions that occur in cells by which fats, carbohydrates, and other compounds are broken down to produce energy and the compounds needed to build new cells and tissues.
- Chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.
FOR FURTHER INFORMATION
Brody, Tom. Nutritional Biochemistry. San Diego: Academic Press, 1998.
"Dietary Supplement Fact Sheet: Vitamin B6." NIH Office of Dietary Supplements. http://ods.od.nih.gov/factsheets/vitaminb6.asp (accessed on November 3, 2005).
Turner, Judith. "Pyridoxine." In Gale Encyclopedia of Alternative Medicine. Detroit: Gale Group, 2004.
Deficiency causes abnormalities of the metabolism of the amino acids tryptophan and methionine; in rats deficiency causes convulsions and skin lesions (acrodynia) and in dairy cows and dogs, anaemia with small, underpigmented red blood cells. Dietary deficiency leading to clinical signs is not known in human beings, apart from a single outbreak in babies fed a severely over‐heated preparation of formula milk in the 1950s; they showed abnormalities of amino acid metabolism and convulsions resembling epileptic seizures, which responded to supplements of the vitamin.
Rich sources include nuts, meat, fish, wholegrain cereals, and beans.
pyr·i·dox·ine / ˌpirəˈdäkˌsēn/ • n. Biochem. a colorless weakly basic solid, C8H11NO3, present chiefly in cereals, liver oils, and yeast, and important in the metabolism of unsaturated fatty acids. Also called vitamin B6.