Around 400 BCE, the celebrated Greek physician Hippocrates offered some advice about diet and health. He declared, "Let food be thy medicine and medicine be thy food." The growing number of Americans who turn to supplements to make up for a poor diet ought to pay attention to those words of wisdom.
Each day, millions of adults in the US take high doses of vitamins and minerals with hopes of feeling better, getting sick less often, and living longer. For years, physicians told consumers that, at worst, they were just wasting their money. But now, the word is to be carefulbecause high doses of certain vitamins and minerals may actually increase the risk of disease.
Dietary Supplements 101
As you probably already know, we need vitaminsby far the most popular choice of supplementto live (that is, they are vital to our survival). But the body cannot produce them on its own, so we must get vitamins from our diet. Similarly, we need minerals like iron and calcium to function, and must rely on outside sources to meet our requirements. (Other supplements, such as herbs and amino acids, are a whole other story.)
Although supplements are a good idea in certain cases (such as for pregnant or breastfeeding women, the elderly, and vegetarians), experts agree the best way for you to get the nutrients you need is by eating a well-balanced, healthful diet.
Too Much of a Good Thing One hundred years ago, scientists began to identify the nutrients in foods that we need to avoid getting deficiency diseases like beriberi and rickets. Since the 1950s, researchers have been uncovering the potential of vitamins and minerals to prevent all sorts of diseases, ranging from cardiovascular disease to cancer. With so much attention being given to the benefits of vitamins and minerals, its no wonder that many of us choose to take supplements. Problems arise, however, when people take individual vitamins or minerals in excessive amounts, rather than eat a nutritious diet. Use the following chart as a guide:Supplements: Recommended Intake Levels of Some Supplements and Known Risks Associated With Excessive AmountsVitamin or MineralWhy You Need ItRecommended Dose (for adults, ages 19-50)Tolerable Upper Intake Level (UL)What Happens if You Overdo ItGood Food SourcesVitamin AVision, growth, and immune function900 micrograms per day (g/d) for men (equivalent to 2,997 International Units), 700 g/d for women (2,333 IU/d)3,000 g/d (10,000 IU/d)Too much may cause hair loss, nausea, and vomiting, and may increase the risk of bone fracture. Very high intakes can cause liver disease and fetal malformations.Preformed vitamin A sources include fortified cereal, eggs, and dairy products; Provitamin A carotenoids (like beta-carotene), found in deep orange and dark green fruits and vegetablesVitamin B6Protein metabolism, neurotransmitter formation, red blood cell function, and hormone function1.3 milligrams per day (mg/d)100 mg/dIf taken at very high doses, may result in painful neurologic symptoms and difficulty walking.Fortified cereals, beans, meat, poultry, fish, and some fruits and vegetablesFolic acid (folate)DNA metabolism as well as the metabolism of several important amino acids400 g/d1,000 g/dHigh doses, while safe in themselves, may mask symptoms of, the rare disease, pernicious anemia allowing it to progress unchecked.Fruits and vegetables, fortified grain foodsNiacinNecessary for energy metabolism16 mg/d for men, 14 mg/d for women35 mg/dIn doses fifty times higher than the tolerable upper intake level, can damage the liver and cause severe gastrointestinal problems.Meat, poultry, fish, fortified cereals, legumes, milk, and seedsVitamin CIt is required for the synthesis of collagen and the neurotransmitter norepinephrine90 mg/d for men, 75 mg/d for women2,000 mg/dGenerally safe, but at high doses can cause diarrhea and might increase risk of urinary tract stones.Citrus fruitsVitamin DIt helps to form and maintain strong bones, plus is needed to maintain blood levels of calcium and phosphorus5 g/d (200 IU/d)50 g/d (2,000 IU/d)Continuous very high intakes might lead to liver and kidney failure.Fatty fish (herring, salmon, sardines), eggs from hens that have been fed vitamin D, and fortified milk; exposure to sunlight provides another important sourceIronAn essential component of hundreds of proteins involved in the transport and storage of oxygen8 mg/d for men, 18 mg/d for women 19-50, 8 mg/d for women older than 5045 mg/dCan poison a child, causing nausea, vomiting, lethargy, fever, difficulty breathing, coma, and even death; in adults excess iron is theorized to increase risk of heart disease.Lean red meats, shellfish, legumes, dried fruit, and green leafy vegetables (Note: iron from non-meat sources is best absorbed when vitamin C is also present)SeleniumNecessary for the function of numerous enzymes55 g/d400 g/dToxic effects of overdosage include hair and nail brittleness and loss, gastrointestinal disturbances, skin rashes, fatigue, irritability, and nervous system abnormalities.Organ meats, seafood, and grainsThe Bottom LineWhile it may be promising, the evidence so far linking supplements with a reduced risk of chronic disease is much less convincing than most people realize. What is clear is just how easy it is to overdose on certain supplements. Therefore, your best bet is to get most of the nutrients you need from the foods you eat. For a healthful diet, be sure to include lots of fruits and vegetables, whole grains (like whole wheat bread and brown rice), unsaturated fats (found in nuts, avocadoes, and oils), and low-fat dairy products.
If you do take supplements, keep the following in mind: A multivitamin wont hurt and is probably a good idea for many people. Choose one that provides no more than 100% of the RDA of each vitamin and mineral.A multivitamin cannot provide adequate calcium, and for this reason many people could benefit from a separate calcium supplement.Be wary of unfounded medical claims for dietary supplements.Talk to your doctor about all supplements you take, including concentrations and amounts.Keep supplements out of the reach of children.RESOURCES:National Institutes of Health, Office of Dietary Supplementshttp://ods.od.nih.govUS Food and Drug Administration, Center for Food Safety and Applied Nutritionhttp://vm.cfsan.fda.govCANADIAN RESOURCES:Canadian Council on Food and Nutritionwww.ccfn.caDietitians of Canadahttp://www.dietitians.ca/References: Micronutrient Information Center, Linus Pauling Institute website. Available at: http://lpi.oregonstate.edu/.Accessed on June 25, 2003. National Academy of Sciences website. Available at: http://books.nap.edu/. Accessed on June 30, 2003. National Academy of Sciences website. Available at: http://www.nap.edu/. Accessed on June 30, 2003.
National Institutes of Health website. Available at: http://www.cc.nih.gov/. Accessed on June 25, 2003. Last reviewed April 2008 by Maria Adams, MS, MPH, RDPlease be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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