Vitamin B6 is a water-soluble vitamin that is found in a variety of forms in the foods we eat as well as in our bodies. These forms include pyridoxal 5′-phosphate (PLP), which appears to be the most active form as a human vitamin. Other forms include pyridoxal (PL), pyridoxamine (PM), pyridoxine (PN), pyridoxamine 5′-phosphate (PMP) and pyridoxine-5′-phosphate (PNP).
There has been substantial debate about blood levels of vitamin B6 and their relationship both to dietary intake and overall health. This debate has centered around the fact that a person can consume the recommended dietary amount of vitamin B6 and yet have a blood level of vitamin B6 (in the form of plasma PLP) that may not be optimal for metabolism. While we continue to recommend the highest adult Dietary Reference Intake (DRI) level for B6 as established by the National Academy of Sciences, we recognize that this amount might eventually be revised upward based on future research in this area. We would also note that the Tolerable Upper Limit (UL) for vitamin B6 is set at a relatively high level of 100 milligrams for adults, allowing plenty of room for B6 intake substantially above the DRI level.
Hemoglobin is complicated protein present in red blood cells, and one of its primary roles is to help carry oxygen around the body. Heme is a key section of the hemoglobin molecule and the initial production of heme in bodies requires the presence of vitamin B6. (Although heme production can occur in multiple places throughout the body, the primary places involve the liver and bone marrow.) The importance of vitamin B6 in red blood cell production is underscored by relatively rare types of anemia called sideroblastic anemias.
Vitamin B6 is involved at several steps in the metabolism of carbohydrates. In particular, the enzyme that pulls carbohydrates out of storage in the cell (in the form of a molecule called glycogen) requires vitamin B6 for its activity.
While nobody would do an experiment like this in humans, researchers have been able to induce problems in carbohydrate metabolism by feeding rats diets deficient in vitamin B6. Since breakdown of carbohydrates is an ongoing process that occurs in our bodies throughout the day to help us sustain our physical energy level, daily consumption of whole foods rich in B6 also makes good sense for maintaining ongoing energy levels.
Vitamin B6 is one of several B vitamins required for proper production of messaging molecules in our nervous system and brain (called neurotransmitters). Three key neurotransmitters—namely GABA, dopamine, and serotonin—all require vitamin B6 for synthesis.
Just as an example of how important this nutrient can be to proper brain and nervous system, function, there is a condition called pyridoxine-dependent epilepsy where a genetic mutation interferes with normal vitamin B6 function. In people who have this mutation, the brain does not develop properly and epileptic seizures are experienced beginning in infancy. Luckily, this condition is rare.
However, we may be at risk of other more common problems that can be brain and nervous-system related if our B6 intake is poor. Depression is a good example in this area. Researchers in Japan have found that the risk of depressed mood is higher in people with lower levels of vitamin B6 in their diet (in comparision with the general population). Another research group concluded that this link between risk of depression and B6 intake becomes even stronger when dietary folic acid—a nutrient that works very closely with vitamin B6 in brain and nervous system chemistry—is deficient as well. Recent research has also begun to indicate a link between B6 deficiency and risk of development for attention deficit disorder (ADHD). So once again, we are looking at the possible widespread importance of B6 for brain and nervous system support.
Generally speaking, we remove unwanted chemicals from our blood in the liver and kidney, and this process involves two steps. The first of these two steps is to make the chemicals more water soluble to allow for the second step of binding and removal. The number of nutrients required for this first step is long, but vitamin B6 is clearly one of the most important. It is so important that researchers can induce liver dysfunction in animals by feeding them a pyridoxine-depleted diet.
Preliminary research on inflammation-related chronic diseases has shown likely connections between the risk of these diseases and B6 deficiency. Interestingly, in addition to increased risk of these conditions in association with B6 deficiency, the presence of chronic inflammatory conditions also appears to be associated with depletion of vitamin B6.
In animal studies, B6 has been shown to play a role in the development of healthy immune system function. This potential health benefit from B6 appears to be associated with its role in metabolism of the amino acid tryptophan.
As mentioned earlier, B6 plays a well-researched role in the synthesis and metabolism of certain nervous system messaging molecules. While we emphasized the nervous system aspects of this health support role earlier in this section, we would also like to point out that the messaging molecules pathways described earlier involve specific amino acids (building blocks of protein), making B6 a potentially important vitamin for support of general amino acid and protein-related metabolism. This overlap may not be a coincidence, given the role played by B6 in protein and amino acid metabolism. It is also worth mentioning that diets especially high in protein may increase risk of B6 depletion, even though many protein-rich foods are also rich in B6. The reason for this risk involves differing nutrient concentrations in which the concentration of protein in a particular food might be significantly greater than the concentration of B6. While this difference might not be important at ordinary protein intakes, unusually high intakes (for example, intakes well over 100 grams) might make the difference more of an issue.