Vitamin B6 or pyridoxine, as part of the water-soluble vitamin B-complex family, is actually a mixture of 6 inter-convertible pyridine vitamers, or related compounds: pyridoxine, pyridoxamine, pyridoxal, and their 5′-phosphorylated forms ⁽¹⁾. Although plants and microorganisms can synthesize B6 on their own, humans must acquire it from dietary sources. Because vitamin B6 is abundant in meats, fish, poultry, shellfish, leafy green vegetables, legumes, fruits, and whole grains, deficiencies are rare. For example, patients taking the antituberculosis drug isoniazide need to take vitamin B6 to prevent drug-induced peripheral neuropathy. Patients may use supplemental B6 to treat symptoms related to heart disease, hypertension, peripheral neuropathies, carpal tunnel syndrome, and diabetes.

Preclinical studies show that systemic administration of certain B vitamins including B6 has neuroprotective, antihypertensive ⁽²⁾, antinociceptive ⁽³⁾, and antitumor effects ⁽⁴⁾. In humans, higher B6 intake may lower serum homocysteine concentrations ⁽⁵⁾ and decrease risk of progression to late age related macular degeneration ⁽⁵⁴⁾ but did not reduce the risk of developing type 2 diabetes ⁽⁶⁾. A systematic review determined that B6 may be useful in treating neuropsychiatric adverse effects associated with the antiepileptic drug Levetiracetam ⁽⁵⁵⁾. High dietary intakes of folate and B6 have been associated with reduced risk of mortality from stroke, coronary heart disease, and heart failure ⁽⁷⁾. Intake of B6 has also inversely associated with metabolic syndrome ⁽⁵⁶⁾. In older adults with mild cognitive impairment taking aspirin, B6 had favorable effects on global cognitive functioning  ⁽⁵⁷⁾.

Studies suggest dietary intake of vitamin B6 may reduce risk for colorectal ^{(14) (15) (16)} and pancreatic cancers ⁽⁴⁷⁾, and lower intakes are associated with increased risk of some gastrointestinal cancers ^(17) (18). Dietary B6 may also reduce risk of ovarian cancer ⁽⁴⁸⁾ and all cancers, although this may occur because of the many other micronutrients that are also ingested ⁽⁴⁹⁾.

Getting B6 through supplements is not associated with the same positive effects on disease risk. Conclusions from the Women’s Health Study indicate that supplementation with B6, B12, and folate did not decrease breast cancer risk ⁽¹⁹⁾, nor did it have an effect on overall risk of invasive cancer or breast cancer ^(20) (21). Long-term supplementation was also associated with increased risk of lung cancer, especially in male smokers ⁽⁴⁶⁾.

Although vitamin B6 has been used empirically to prevent or treat chemotherapy-associated hand-foot syndrome (HFS), several randomized trials did not find benefit ^{(22) (23) (24) (25) (50) (51)}. But higher doses may have benefit ^(26) (58).  In one study, it did reduce the need for capecitabine dose modifications and incidence of severe HFS, but did not positively impact chemotherapy effects ⁽²⁷⁾.

High intakes of vitamin B6 can have toxic effects including sensory and motor neuropathies, and some case reports of neurotoxicity have not been reversible ^(29) (52). In addition, a secondary analysis among postmenopausal women in the Nurses’ Health Study found that combined high intakes of B6 and B12 were associated with an unexpected increased risk of hip fracture ⁽⁵³⁾. Large quantities of vitamin B6 should also be avoided in women who are pregnant or of childbearing potential ⁽¹³⁾.