Vitamin B6 is a group of closely related water-soluble compounds, most commonly referred to simply as pyridoxine, that are essential in numerous biochemical pathways involving red blood cells, the immune system, central nervous system function, protein metabolism, homocysteine metabolism, and also the production of energy.
      More specifically, vitamin B6 consists of six specific compounds, namely pyridoxine, pyridoxal, pyridoxamine, and their respective phosphates, the latter group of which are the most active components in numerous reactions involving amino acid and protein metabolism.

      The most recent research on vitamin B6 suggests a RDA of 1.3 mg for adult males, and 1.2 mg for adult females, somewhat less than the RDI of 2.0 mg referenced on current food labels. The more detailed figures from the recent National Academy of Sciences Dietary Reference Intakes study are based upon slightly different age ranges than those previously reported, accounting for the overlapping groups in the following table.

      The primary food sources for the compounds of vitamin B6 include fortified cereals, starchy vegetables (such as white potatoes), non-citrus fruits, eggs, beef liver, fortified soy-based meat substitutes, other meats, poultry and fish, beans, and nuts.

      The symptoms most often associated with vitamin B6 deficiency include dermatitis (specifically, seborrhea-like lesions in the area of the eyes, nose and mouth), decreased hemoglobin production leading to anemia and its effects, and central nervous system disorders resulting in convulsive seizures. These manifestations are relatively uncommon in populations enjoying normal diets, and occur primarily in clinical situations and among individuals whose socio-economic conditions prevent the dietary intake recommended for vitamin B6.
      Vitamin B6 deficiency is also known to increase serum and plasma homocysteine levels, a compound which is becoming increasingly more closely associated with potential for risk of heart disease (see Current Issues).

      Supplemental vitamin B6 is most commonly used to contribute to dietary intake, but has also been used for a wide range of maladies, some of which without an apparent, reasonable scientific relationship to the vitamin (see Current Issues below).
      Vitamin B6 is found in most multivitamins, typically in dosages of 2.0 mg, which is 100% of the current Reference Daily Intake (RDI). It can also be found as a standalone supplement, some which have very high dosages, and commonly in combination with other vitamins of the B complex (folate and vitamin B12, in particular) which appear to enhance B6's effect on plasma homocysteine levels (see Current Issues).

      The health risks reported for vitamin B6 are primarily the result of intakes of very large supplemental amounts of the vitamin as pyridoxine. The most common symptoms are nervous system disorders (primarily balance problems, numbness in the extremities and difficulty with walking) and skin lesions.
      In light of some of the potential hazards resulting from excessive doses of vitamin B6, the most recent National Academy of Sciences Dietary Reference Intakes study has reported a Tolerable Upper Intake Level (UL) for adults of 19 years and older of 100 mg/day for this vitamin.

      Supplemental vitamin B6 has been prescribed and administered for a wide range of apparently unrelated maladies and disorders for many years. Among the reported uses include relief from carpal tunnel syndrome, premenstrual syndrome, and morning sickness. Unfortunately, there is no conclusive evidence that this use of the vitamin is consistently effective. In fact, such use in clinical settings more commonly produced health defects rather than the positive results intended. The best advice is to consult with your health care provider.
      A few studies have also been conducted on measuring the effects of supplemental vitamin B6 on cognitive function in the elderly. Likewise, the results have not been conclusive and require additional research.
      On the other hand, a widely reported effect of supplemental vitamin B6 use is the reduction of plasma homocysteine levels, a compound that is now believed to play a significant role in vascular disease. Collectively, numerous studies have concurred that increased dietary and supplemental vitamin B6 has the potential to reduce the risk factor of vascular disease by as much as 30 percent. When taken in combination with other vitamins of the B complex, folate and vitamin B12 in particular, the apparent risk reduction for heart disease is even higher.
      While these reports are very promising, the recent National Academy of Sciences Dietary Reference Intakes study on vitamin B6 indicates there is insufficient data to recommend an effective supplemental intake in this regard. One report suggests, and individuals should be so cautioned, that vitamin B6's apparent effect on lowering plasma homocysteine levels does not steadily increase as the dosage of vitamin B6 increases. Instead, there appears to be an optimal intake that is no more than several times the DRI for vitamin B6 that is most effective.
      It has also been suggested that increased levels of dietary protein have a negative effect on the absorption of vitamin B6. This would mean that individuals on high protein diets would have to increase their vitamin B6 intake to offset the malabsorption factor. These reports are not completely consistent, in part due to the effects of other dietary and metabolic factors.