Vitamin B6 includes a group of closely related compounds: pyridoxine, pyridoxal, and pyridoxamine. They are metabolized in the body to pyridoxal phosphate, which acts as a coenzyme in many important reactions in blood, central nervous system, and skin metabolism. Vitamin B6 is important in heme and nucleic acid biosynthesis and in lipid, carbohydrate, and amino acid metabolism (see table Sources, Functions, and Effects of Vitamins).
Dietary sources of vitamin B6 include organ meats (eg, liver), whole-grain cereals, fish, and legumes. (See also Overview of Vitamins.)
Etiology
Dietary vitamin B6 deficiency, though rare, can develop because extensive processing can deplete foods of vitamin B6.
Secondary vitamin B6 deficiency most often results from
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Use of pyridoxine-inactivating drugs (eg, antiseizure drugs, isoniazid, cycloserine, hydralazine, corticosteroids, penicillamine)
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Excessive loss during hemodialysis
Rarely, secondary deficiency results from increased metabolic demand (eg, in hyperthyroidism).
Rare inborn errors of metabolism can affect pyridoxine metabolism.
Symptoms and Signs
Vitamin B6 deficiency causes peripheral neuropathy and a pellagra-like syndrome, with seborrheic dermatitis, glossitis, and cheilosis, and, in adults, can cause depression, confusion, electroencephalogram abnormalities, and seizures.
Rarely, deficiency or dependency causes seizures in infants. Seizures, particularly in infants, may be refractory to treatment with antiseizure drugs.
Normocytic, microcytic, or sideroblastic anemia can also develop.
Diagnosis
Treatment
For secondary vitamin B6 deficiency, causes (eg, use of pyridoxine-inactivating drugs, malabsorption) should be corrected if possible.
Usually, pyridoxine 50 to 100 mg orally once a day corrects the deficiency in adults. Most people taking isoniazid should also be given pyridoxine 30 to 50 mg orally once a day. For deficiency due to increased metabolic demand, amounts larger than the daily recommended intake may be required. For most cases of inborn errors of metabolism, high doses of pyridoxine may be effective.
Key Points
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Vitamin B6 deficiency is usually caused by pyridoxine-inactivating drugs (eg, isoniazid), protein-energy undernutrition, malabsorption, alcoholism, or excessive loss.
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Deficiency can cause peripheral neuropathy, seborrheic dermatitis, glossitis, and cheilosis, and, in adults, depression, confusion, and seizures.
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Suspect and diagnose based on clinical findings.
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Correct secondary causes, or give supplemental pyridoxine.
