& Joannie Dobbs Saturday
October 20, 2007
Though B6 is important, don't overdose
Vitamins are required in such tiny amounts that some people think it is almost impossible to not get enough. In contrast, others believe that vitamins are safe at any dosage sold. Both would be wrong in the case of vitamin B6.
Question: What is vitamin B6?
Answer: Vitamin B6 is also known as pyridoxine, pyridoxal and pyridoxamine. This vitamin is required for more than 100 enzymes essential for body functions. For example, B6 is needed to make blood, to keep the nervous system and the immune system functioning properly, and to regulate blood glucose levels.
Q: How much vitamin B6 does a person need?
A: The Institute of Medicine currently recommends 1.3 milligrams per day for those between the ages of 19 and 50. For those older than 50, the recommendation increases slightly to 1.5 mg for women and 1.7 for men. When a label for a dietary supplement or fortified food indicates 100 percent of the "Daily Value," the product contains 2 mg of vitamin B6 per serving (usually one pill).
Q: What are the symptoms of a vitamin B6 deficiency?
A: This deficiency is rare in the United States. However, many older Americans have low blood levels of the vitamin, indicating a marginal intake. Clinical signs of deficiency include skin inflammation, sore tongue, depression, confusion and even convulsions. Vitamin B6 deficiency also can lead to anemia.
Q: What are the symptoms and consequences of megadoses?
A: Unfortunately, high doses of this vitamin, if taken for too long, can have serious consequences. Excess B6 damages nerves -- especially those in the arms, hands, legs and feet. Symptoms include coordination problems along with sensations of numbness and tingling.
This neuropathy, or nerve problem, resolves gradually after supplementation is stopped, but has resulted in permanent damage in a few cases.
The Institute of Medicine set the tolerable upper intake level for B6 at 100 mg per day from food and supplements combined. However, the Expert Group on Vitamins and Minerals in the United Kingdom established a safe upper limit from supplements at 10 mg per day -- one-tenth the U.S. limit.
A recent case study reported that a woman developed serious neuropathy from taking 100 mg per day for 10 years. So the level of intake for long-term safety is likely lower than the U.S. upper limit of 100 mg.
Many foods contain vitamin B6. Consequently, B6 deficiency is unlikely unless the diet is extremely limited in variety or total food consumed.
Alan Titchenal, Ph.D., C.N.S. and Joannie Dobbs, Ph.D., C.N.S.
are nutritionists in the Department of Human Nutrition, Food and Animal Sciences,
College of Tropical Agriculture and Human Resources, UH-Manoa.
Dr. Dobbs also works with the University Health Service
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