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Effects From Taking Large Doses of Vitamin & Mineral Supplements

By Lisa Sefcik

Vitamins and minerals may seem harmless when taken in pill form. These are classified by the U.S. Food and Drug Administration as dietary supplements. However, taking megadoses of vitamin and mineral supplements usually isn't necessary if you're in good health. In some cases, this can cause ill effects and compromise your health.

Your Need for Supplements

According to Harvard Medical School, more than half of Americans take vitamin and mineral supplements. However, there's very little research that shows these are beneficial to your health, even when taken in regular doses. The only exceptions to the rule may be fish oil and vitamin D supplements, says Harvard. If your diet includes an abundance of vegetables, fruit, nuts, whole grain foods and fish, you're likely getting your essential nutrients. Some people may choose to take a multivitamin as a fallback; however, taking large doses of a vitamin or mineral can lead to adverse side effects and health consequences.


According to Baylor College of Medicine, water-soluble vitamins usually aren't problematic when taken in large doses, as these are flushed from the body through the kidneys. However, the fat-soluble vitamins A, D, E and K are may be problematic. Too much vitamin A, or beta-carotene, is associated with an increased risk of certain cancers and other health problems in people who smoke or who are exposed to asbestos. Vitamin D deficiency can cause a condition called hypercalcemia, in which too much calcium is released in your blood, according to Nausea and vomiting, constipation, weakness and confusion are some symptoms associated with vitamin D toxicity. When taken in large amounts, vitamin E is associated with stroke and premature death. Water-soluble vitamins such as vitamin C may not be as dangerous. However, taking megadoses of it isn't beneficial. A February 2006 National Public Radio report described taking large quantities of vitamin C for colds as one of the "greatest hoaxes ever played on the American public."


Taking megadoses of minerals can also cause harmful effects. Dr. Herb Denenberg, a professor at the Wharton School and Institute of Medicine of the National Academy of Sciences member, indicates that large doses of iron are linked to organ damage caused by a common hereditary disease called hemachromatosis as well as compromised heart and neurologic health. Megadoses of zinc can result in iron deficiency, gastritis and changes in your blood cholesterol, and too much potassium can cause heart failure and even prove fatal. Large doses of magnesium may have the same effect as taking a laxative.

Choosing Supplements

According to Denenberg, taking a multivitamin can serve as your nutritional "insurance policy." Certain populations, such as pregnant women and the elderly, may benefit from taking dietary supplements as well. However, avoid megadoses of any one vitamin or mineral. indicates that you should pass over those that give you 500 percent of your daily value for one vitamin or mineral and 20 percent of your DV for another. Look for a supplement that gives you no more than 100 percent of your DV for vitamins and minerals, with the exception of calcium. If your supplement contained 100 percent of your DV for this mineral, it would be too large to swallow.

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