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Q&A: Are megadoses of B vitamins dangerous?

Consumer Reports News: November 03, 2009 06:08 AM

I take a multivitamin containing 1,000 to 3,000 percent of the daily value of vitamins B12, B6, thiamin, and riboflavin. Are such doses dangerous? --A.R., Riverside, Calif.

Probably not, but for healthy people there's little or no evidence that megadoses of those B vitamins are useful, either. Only B6 has been linked to a possible side effect, nerve damage. And that was at higher doses--7,000 percent of the daily value (DV), taken long-term--than you're taking. Megadoses of B12 appear to be safe, since studies of pernicious-anemia treatment with injections of more than 40,000 percent of the DV haven't reported any side effects. Thiamin and riboflavin also appear harmless because the body absorbs only a fraction of the huge doses; the rest is excreted in the urine.

Read more on  getting vitamins and nutrients from the foods you eat , and for more on the safety and effectiveness of B vitamins, take a look at our Natural Medicine Ratings  (subscribers only).

Aaron Bailey

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