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| B6 |
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Vitamin B6 is the term for three related compounds, pyridoxine, pyridoxal and pyridoxamine and their phosphorylated derivatives. These are pyridoxine 5'-phosphate, pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate. Vitamin B6 technically refers to all six of these vitamers, although vitamin B6 is used interchangeably with pyridoxine. Pyridoxine, pyridoxine 5'-phosphate and pyridoxine glucosides are found in plant foods. The other vitamers, primarily pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate, are found in animal products. Glycosylated pyridoxine forms of vitamin B6 range from 5 to 75% of the total vitamin B6 content in fruits, vegetables and grains. There is very little or none of the glycosylated pyridoxine form of vitamin B6 in animal products. Vitamin B6 is soluble in water and stable to heat and acid. However, oxidation and exposure to alkali and UV light destroy vitamin B6. As much as 50% of vitamin B6 is destroyed during cooking and processing. The coenzyme pyridoxal 5'-phosphate is involved in a wide range of biochemical reactions. These include the metabolism of glycogen and amino acids, the synthesis of nucleic acids, and the synthesis and metabolism of hemoglobin. It is also involved in the synthesis of sphingomyelin and other sphingolipids and neurotransmitters (serotonin, dopamine, norepinephrine, histamine and gamma-aminobutyric acid). Pyridoxal 5'-phosphate is involved in the metabolism of gamma-aminobutyric acid, which is a major inhibitory neurotransmitter in the central nervous system. Vitamin B6 in the form of pyridoxal 5'-phosphate acts as a coenzyme for more than 100 enzymes. The signs and symptoms of vitamin B6 deficiency are microcytic, hypochromic anemia, seizure activity, seborrheic dermatitis, confusion and depression. Deficiency of vitamin B6 in children and infants results in electroencephalogram abnormalities and seizure activity. Deficiency of vitamin B6 in adults results in cheilosis, glossitis, stomatitis, anemia, irritability, confusion and depression. Secondary deficiencies of vitamin B6 may result from malabsorption, uremia, cancer, heart failure, and cirrhosis. Adolescent females during pregnancy, the elderly, and alcoholics are populations at risk for secondary vitamin B6 deficiency. Other vitamin B6 deficiencies may result from chemical inactivation, excessive vitamin B6 loss, or increased metabolic activity associated with the use of some medications (e.g., isonicotinic acid hydrazide, penicillamine, cycloserine, thionamide, hydralazine and theophylline). Although there are benefits from megadoses of vitamin B6 in selective individuals, the use of high doses of pyridoxine may have some risk. Adults chronically ingesting megadoses of 2 to 6 g/day of pyridoxine may experience progressive sensory neuropathy. Excessive amounts of pyridoxine appear to cause the degeneration of dorsal root ganglia. Good food sources of vitamin B6 are meat, poultry, fish, eggs, white potatoes and starchy vegetables. Noncitrus fruits (such as bananas), navy beans, walnuts, fortified cereals and fortified soy meats are also sources of vitamin B6. The RDA for vitamin B6 is 1.3 mg a day for men and women under age 50. For those over 50, the RDA is 1.7 mg for men and 1.5 mg for women. Taking high doses of this vitamin (more than 200 mg daily) over the long term may cause nerve damage. If you take vitamin B6 for nerve pain and develop any new numbness or tingling, stop taking the supplement and consult your doctor. Vitamin B6 supplements (25 mg a day) are commonly recommended for relieving the nausea and vomiting of pregnancy-related morning sickness. However, because there is still so little data on how such supplements will affect your developing baby, consult your doctor before taking the supplement. |