Vitamin B-6 is found in three related forms in food -- pyridoxine, pyridoxal and pyridoxamine -- all of which are attached to a phosphate group when they get into your tissues. Nutritionist Dr. Elson Haas reports that pyridoxal phosphate is the most biologically active form of vitamin B-6. Like other B vitamins, vitamin B-6 is water-soluble, meaning it is easily eliminated in your urine. Therefore, toxicity due to B-6 is unlikely at reasonable daily doses, but regular consumption of as little as 200 mg could cause adverse effects.
Vitamin B-6, as the coenzyme pyridoxal-5-phosphate, serves in an impressive array of physiologic functions. It is needed for the utilization of all food sources -- carbohydrates, fats and proteins -- and for the release of stored energy molecules from your liver and muscles. B-6 is instrumental in amino acid metabolism, antibody production, DNA and RNA synthesis and hemoglobin production. Several neurotransmitters, such as GABA, serotonin, norepinephrine and acetylcholine, require vitamin B-6 for their metabolism, and B-6 helps to maintain the normal balance of sodium, potassium and magnesium in your cells.
Some of the best sources of vitamin B-6 are meats, especially organ meats. However, B-6 is destroyed during cooking, so it is not easily acquired from animal sources. Whole grains and wheat germ are good sources, as are soybeans, peanuts, walnuts, dried beans, bananas, prunes, potatoes, bell peppers, cruciferous vegetables and mushrooms. Raw sugar contains a fair amount of B-6, while refined sugar has none. Overdose of vitamin B-6 from food sources has not been reported.
In 2000 the National Academy of Sciences established recommended dietary allowances for vitamin B-6. Such RDAs are useful guidelines, but your need for vitamin B-6 may vary, depending on your diet, physical activity and other factors. For example, a study published in the July 1, 1996, edition of “The Journal of Nutrition” demonstrated that a woman’s vitamin B-6 requirements change with different levels of protein consumption. Oral contraceptives also increase a woman’s vitamin B-6 requirements. Current RDAs for vitamin B-6 range from 100 mcg for infants to 2 mg for lactating women.
Symptoms of toxicity have been noted in people taking large doses of supplemental vitamin B-6. Regular intake of more than 1,000 mg daily is often associated with a reversible neuropathy that is characterized by weakness and pain, numbness or tingling in the extremities. These symptoms resolve with reduction of B-6 intake. Although no study has shown human toxicity when daily vitamin B-6 intake is below 200 mg, the National Academy of Sciences has established a tolerable upper limit of 100 mg daily for adults.