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    How do I know if I'm deficient in an important vitamin or mineral?

    Answer by:
    David Kiefer, MD

    Family Medicine, WebMD Medical Expert
    University of Arizona, Tucson

    Some vitamin or mineral deficiencies can cause symptoms such as fatigue, pallid-looking skin, brittle hair or fingernails, diarrhea, memory problems, and a weakened immune system. But most deficiencies have to be extreme or have to continue for a long time to cause noticeable problems. If you're worried about vitamin or mineral deficiencies, talk to your doctor. Tests are available to measure levels of key vitamins or minerals such as vitamin D, B12, or iron.

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