Vitamin B6

Vitamin B6, or pyridoxine, is a water-soluble vitamin and a coenzyme in the folate metabolism pathway. Phosphorylated metabolites of pyridoxine are involved in amino acid metabolism, the transsulfuration pathway of homocysteine to cysteine, and glycogen phosphorylase, which mobilizes glucose from glycogen ⁽²⁾. Vitamin B6 is abundant in meats, fish, poultry, shellfish, leafy green vegetables, legumes, fruits, and whole grains. Patients use vitamin B6 for heart disease, hypertension, peripheral neuropathies, carpal tunnel syndrome, and diabetes. Preliminary data suggest that vitamin B6 may be of benefit for palmar-plantar erythrodysesthesia (PPE) ⁽⁵⁾ and carpal tunnel syndrome ^{(7) (8)}, but additional studies are necessary. Studies of its efficacy in diabetes ⁽⁶⁾, heart disease ^{(9) (10)}, premenstrual syndrome ^{(11) (12) (13)}, and hypertension ⁽¹⁴⁾ show inconsistent results. Vitamin B6 supplementation was not effective in improving cognition in older adults ⁽¹⁸⁾.

Current data suggest a beneficial role of vitamin B6 in preventing colorectal cancer ^{(15) (16) (21)} and an inverse association was reported between vitamin B6 and risk of gastric adenocarcinoma ⁽²⁰⁾. However, conclusions from the Women's Health Study indicate that supplementation with vitamins B6, B12, and folate did not decrease the risk of breast cancer ⁽¹⁷⁾ and a recent study reported that a combination of folate and vitamins B6 and B12 did not have an effect on overall risk of invasive cancer or breast cancer ⁽¹⁹⁾. Vitamin B6 administration is also ineffective in preventing chemotherapy associated hand and foot syndrome ^{(22) (23)}.

Infrequent adverse events include headache, nausea, sedation, and mild paresthesias ⁽³⁾. Chronic consumption of large doses may cause severe neuropathies ⁽²⁴⁾, ataxia, respiratory difficulties, and profound sedation, although reversal usually occurs following discontinuation ⁽⁴⁾.