Q. Is there such a thing as getting too many vitamins? Can you take too much vitamin A or E, for example? If so, what are the side effects? I understand that vitamin C is water soluble and that excessive amounts should be eliminated in the urine. Does this mean that it's virtually impossible to overdose on large amounts of vitamin C?
A. As with many things, too much of a good thing can be harmful. Vitamins are no exception.
There are two classes of vitamins, based on whether the vitamin dissolves in water or fat. Fat soluble vitamins -- A, D and E -- are stored chiefly in the liver. They aren't easily eliminated, so taking large doses over long periods of time could lead to a toxic build-up.
Water-soluble vitamins are eliminated in the urine. They don't tend to accumulate, and so they aren't as much a potential problem. But excessive doses of even these vitamins could spell trouble. Of the fat soluble vitamins, excessive doses of A and D can cause the most problems. The adverse effects would depend on your age (child or adult) and on how much you took over what period of time.
Vitamin A toxicity can damage your liver, making you feel tired and sick to your stomach. You can also get chronic headaches, dizziness, leg swelling, skin that's itchy and scaly, hair loss and joint pains.
Vitamin D toxicity will raise the calcium level in your blood, which in itself is harmful. High calcium levels can make you feel nauseated, weak, achy and confused. Vitamin E is generally safe, even in large doses. But excessive amounts can lead to fatigue, weakness, nausea, headache and diarrhea.
Water-soluble vitamins usually don't cause problems, but in huge doses they can. Many people take vitamin C to treat or prevent colds (a treatment most physicians don't believe works). But vitamin C in massive doses can make you develop painful kidney stones. As another example, large doses of vitamin B-6 can temporarily damage your nerves, causing numbness and difficulty using some of your muscles.
If you take vitamins, I'd suggest not exceeding the Recommended Dietary Allowances unless advised to do so by your physician. The average RDA's of selected vitamins for adults, along with their minimum toxic doses, are listed in the table. The minimum toxic dose is the smallest dose at which someone could ordinarily be expected to have some adverse effect. Some people can take more than this dose without a problem, although I don't recommend doing so.
Jay Siwek, a family physician from Georgetown University, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.
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