Symptoms of vitamin B6 deficiency include seborrheic dermatitis, glossitis, stomatitis, and cheilosis, as frequently seen with other B vitamin deficiencies. In addition, severe Pyridoxine deficiency can lead to generalized weakness, irritability, peripheral neuropathy, abnormal electroencephalograms, and personality changes including depression and confusion. In infants, diarrhea, seizures, and anemia have been reported. Microcytic, hypochromic anemia is due to diminished hemoglobin synthesis, since the first enzyme involved in heme biosynthesis (amino-levulinate synthase) requires PLP as a cofactor. In some case reports, platelet dysfunction has also been reported. Since Pyridoxine is necessary for the conversion of homocysteine to cystathionine, it is possible that chronic low-grade vitamin B6 deficiency may result in hyperhomocystinemia and increased risk of cardiovascular disease.
Certain medications such as isoniazid, L-dopa, penicillamine, and cycloserine interact with PLP due to a reaction with carbonyl groups. Oral contraceptives have been reported to decrease vitamin B6 status indicators, although the mechanism for this is uncertain. Alcoholism also decreases vitamin B6 status due to poor diet, liver disease, and the fact that acetaldehyde can compete with PLP for protein binding, leading to increased degradation and excretion. The increased ratio of aspartate aminotransferase (AST or SGOT) to alanine aminotransferase (ALT or SGPT) seen in alcoholic liver disease reflects the relative vitamin B6 dependence of ALT. Vitamin B6 requirements are higher in preeclampsia, eclampsia, and hemodialysis. Vitamin B6 dependency syndromes that require pharmacologic doses of vitamin B6 are rare, but include cystathionine b-synthase deficiency, pyridoxine-responsive (primarily sideroblastic) anemias, and gyrate atrophy with chorioretinal degeneration due to decreased activity of the mitochondrial enzyme ornithine aminotransferase. In these situations, 100 to 200 mg/d of oral vitamin B6 are required for treatment.
High doses of vitamin B6 have been used to treat carpal tunnel syndrome, premenstrual tension, schizophrenia, autism, and diabetic neuropathy but have not been found to be effective.
The laboratory diagnosis of vitamin B6 deficiency is generally made on the basis of low plasma PLP values (<20 nmol/L). Other measures of vitamin B6 deficiency include low erythrocyte levels of PLP, low plasma pyridoxal, and low urinary levels of 4-pyridoxic acid. Treatment of vitamin B6 deficiency is 50 mg/d; higher doses of 100 to 200 mg/d are given if Pyridoxine deficiency is related to medication use. Vitamin B6 should not be given with L-dopa, since the vitamin interferes with the action of this drug.