Vitamin B6 or pyridoxal, pyridoxine, pyridoxamine and phosphates + Food Sources of Vitamin B6 + Roles of Vitamin B6 + RDAs
What is vitamin B6?
Vitamin B6 is the general name for six compounds pyridoxal (PL), pyridoxine (PN), pyridoxamine (PM), and their phosphate derivatives including pyridoxal 5’-phosphate (PLP), pyridoxine 5’-phosphate (PNP), and pyridoxamine 5′-phosphate (PMP). It is the PLP form that is the most significant in human operations. While long recognized for its pivotal role in the processing of amino acids, vitamin B6 has received attention for its role in homocysteine metabolism and reducing cardiovascular disease risk.
What foods provide vitamin B6 and what form is found in supplements? One form of vitamin B6 is pyridoxine, which is mostly found in plant foods, with better sources being bananas, navy beans, and walnuts. The remaining four forms of vitamin B6 are found mostly in animal foods with good sources being meats, fish, and poultry (Vitamin B6 in Food Table). While vitamin B6 is fairly well absorbed from the small intestine however vitamin B6 from animal sources may be better absorbed than B6 from plant sources. In addition, vitamin B6 is fairly stable in cooking processes; however, some losses are experienced with prolonged exposure to heat, light, or alkaline conditions.Vitamin B6 is available primarily as pyridoxine hydrochloride in multivitamin, vitamin B-complex, and vitamin B6 supplements.
What does vitamin B6 do in the body?
Vitamin B6 can be found in nearly if not all cells throughout the body with higher concentrations found in muscle and liver tissue. Similar to most of its water-soluble vitamin siblings, vitamin B6 is primarily lost from the body in urine. Once inside the cells, vitamin B6 forms can be converted to the active forms of vitamin B6, PLP (pyridoxal phosphate) and PMP (pyridoxamine phosphate). PLP and PMP are key participants in many cell reactions. By and large the most significant roles of vitamin B6 are:
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Amino acid metabolism- Vitamin B6 is crucial for the processing of amino acids including the production of nonessential amino acids made from other amino acids. During this process, the nitrogen-containing amine portion of an amino acid is transferred to a specific molecule (see Vitamin B6 and Amino Acids Figure), which creates a nonessential amino acid. In fact, if an individual developed a vitamin B6 deficiency, most of the nonessential amino acids would actually become dietary essentials.
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Glycogen breakdown - Glycogen breakdown in muscle requires vitamin B6. Glycogen is stored glucose and the breakdown of this complex provides invaluable fuel during exercise and work.
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Neurotransmitter production – Vitamin B6 is also necessary to convert certain amino acids into neurotransmitters gama-amino-butyric acid (GABA) and serotonin.
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Hemoglobin- Vitamin B6 is crucial for the normal production of hemoglobin, the O2 carrying protein found in RBCs. Immunity- In addition, vitamin B6 is essential in the formation of hemoglobin and white blood cells. Finally, vitamin B6 also seems to be necessary to break down glycogen stores during exercise and fasting.
What are the recommended intake levels of vitamin B6?
The adult RDA is 1.3 mg of vitamin B6 for women and men 18 to 50 years of age. After 50 the recommendation increases 1.5 and 1.7 mg daily for women and men respectively. Meanwhile during pregnancy and lactation the recommendation increases for women to 1.9 and 2.0 mg of vitamin B6 respectively. LIke other vitamins the RDA can be viewed as a minimum target intake level. The bottom line is that the metabolism of every amino acid at some point or another will encounter a chemical reaction requiring vitamin B6 as a coenzyme. In fact, vitamin B6 is so deeply rooted in the metabolism of amino acids that the RDA is based on the typical protein content of the American diet. Approximately 0.016 mg of vitamin B6 is apportioned per gram of protein in our diet. Therefore, since the typical daily protein intake of an American adult is approximately 100 to 125 g of protein, this translates to about 1.6 to 2 mg of vitamin B6. For athletes consuming more protein and with higher glycogen stores more vitamin B6 is warranted and accounted for if vitamin B6 intake is based on grams of protein intake. See DRI/RDA Tables for recommended minimum levels for vitamin B6 for people of all ages.
What happens if too little vitamin B6 is consumed?
Deficiency of vitamin B6 is unlikely due to the popularity of meat, fish, and poultry as components of the American diet. However, if a deficiency occurred, amino acid metabolism would be greatly restrained, leading to poor protein synthesis. The production of hemoglobin, white blood cells, and many neurotransmitters would also be greatly hindered. Therefore the signs of a vitamin B6 deficiency would significantly affect human body functions at many levels, including growth, immunity, and reproduction.
Can vitamin B6 be toxic?
The Tolerable Upper Limit has been set at 100 mg daily for both men and women with lower levels for children and during pregnancy and early lactation. If vitamin B6 is consumed in gram doses (2 to 6 g) over many months, it can affect nervous function and possibly lead to irreversible damage to nervous tissue. At one time, vitamin B6 was considered a possible treatment for premenstrual syndrome (PMS), but this concept has since been abandoned and should not be pursued due to lack of promising supportive research and the potential for toxicity.
