A daily multivitamin probably won't harm you. Harvard Medical School's Dr. Walter Willett, head of the school's nutrition department, recommends this "nutritional insurance" just in case you don't get your daily allotment of vitamins and minerals from the food you eat. When taken in doses that are toxic, however, vitamins and minerals can be extremely detrimental to your health. Play it safe, and don't take dietary supplements in excessive amounts, even if you suspect you may have a vitamin or mineral deficiency. Talk to your treating physician instead.
Vitamins
Unlike water-soluble vitamins that are quickly eliminated from your body, fat-soluble vitamins are stored in your body fat and liver and are more likely to be toxic, states the Colorado State University Extension. These potentially toxic vitamins are vitamins A, D, E and K. There are no reported cases of vitamin K toxicity, and too much vitamin E may make you feel nauseated; however, vitamins D and A are more problematic. Severe vitamin D toxicity, although rare, can cause too much calcium in the urine and blood. Symptoms may include weight loss and fatigue, nausea and/or vomiting, constipation and/or diarrhea and an abnormal heart rate. Vitamin A toxicity can cause symptoms that range from nausea and blurry vision to more serious symptoms, including hair loss, bone pain, delayed growth, intercranial pressure and problems with the liver and spleen.
Minerals
Chromium, copper, iodine, iron, fluorine, manganese, molybdenum, selenium and zinc are the nine essential minerals you need for optimal health -- but only in small amounts. The Merck Manuals Online Medical Library notes that all of these minerals have the potential to be toxic if you consume too much of them. Toxic levels of iodine can affect thyroid function. Iron toxicity can result in diabetes and cirrhosis of the liver. Too much manganese may result in symptoms similar to those seen in Parkinson's disease, and taking excessive amounts of calcium can affect how well your body absorbs iron and other minerals. It doesn't take too much work for certain mineral supplements to do their damage; the State Government of Victoria's Better Health Channel indicates that toxicity can result if you take only five times the recommended dietary intake, or RDI, of iron, zinc, chromium and selenium.
Cautions
Some dietary supplements may contain vitamins and minerals in megadoses. In March 2011, the U.S. Food and Drug Administration issued a press release warning consumers to avoid Soladek vitamin, a liquid supplement imported from the Dominican Republic that contains toxic levels of vitamins A and D. Seven people filed reports with the agency complaining of vomiting, diarrhea, impaired kidney function, fatigue, high levels of blood calcium and heart arrhythmia. If you take a combination multivitamin-mineral dietary supplement, go for a reputable brand name. Choose one that gives you at or around 100 percent of your daily value, or DV, for all essential nutrients, states the Mayo Clinic. You won't find a dietary supplement that gives you 100 percent of your DV for calcium, as the pills would be prohibitively large and impossible to swallow. Avoid multivitamins that give you excessively large doses of one or a few vitamins and minerals.
Choice
Vitamin and mineral toxicity can easily be avoided if you don't self-treat medical conditions with dietary supplements. Harvard Medical School states that with the availability of a large selection of foods, as well as vitamin- and mineral-fortified foods, you should be able to get your essential nutrients by eating a varied diet. Multivitamins may be appropriate for certain people, such as postmenopausal women, people who eat less than 1,600 calories a day, pregnant women and vegans or vegetarians. If you're concerned that your diet is lacking the essentials, talk to your doctor, dietitian or nutritionist to see if a multivitamin is appropriate for you.
References
- Harvard Medical School: Multivitamins -- Should You Buy This insurance?; September 2006
- Colorado State University Extention: Fat-Soluble Vitamins; J. Anderson, L. Young; August 2008
- Vitamin D Council: Vitamin D Toxicity; May 2011
- Merck Manuals Online Medical Library: Mineral Deficiency and Toxicity; August 2008
- Mayo Clinic; Multivitamins-Are They the Best Thing for You?; J. Nelson, K. Zeratsky; March 2008
- Mayo Clinic: Dietary Supplements -- Nutrition in a Pill?; June 2010
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