Fit Or Fat: Nutrition and Exercise
Is It Possible To Overdose On Vitamins?
Posting Date: 08/31/2000
Q: Is it possible to get too much of a vitamin? If I eat well and take vitamins is it possible to overdose?
A: Yes. Because vitamins occur naturally in our food, we think they can't hurt us when we take them as pills. But we can see that they can.
For example, you can overdose on vitamin A pills, but you can't overdose on real foods high in vitamin A like carrots. Carrots contain beta-carotene which your body must first convert into an active form of vitamin A. But this process is not very efficient, so you wouldn?t get a toxicity this way. You'll get yellowish skin due to the pigments in beta-carotene, but this is not harmful.
When I was a teenager, cod liver oil was so popular that parents were forcing it on their kids and the resultant vitamin A and vitamin D toxicity deaths became a national scandal.
All the fat-soluble vitamins (A, D, E, K) are stored in the body's fat deposits so that toxic levels are easily attained. Overdose of the B vitamins and vitamin C can occur if you are taking megadoses from supplements, but it?s less likely because they are water-soluble and therefore quickly excreted in the urine.
Vitamin A toxicity is particularly interesting: 100,000 International Units (IU) per day produce brain damage and death in laboratory rats. (For simplicity, I use the human equivalent of the rat dosage.) Naturally, researchers wanted to know what dosage the rats could take without getting such drastic effects. They kept diminishing the dose until, at 50,000 IU per day, the rats suffered no ill effects at all.
With 5000 IU being the RDA level and 100,000 IU the severely toxic, 50,000 IU seemed to be a maximum safe dosage. One university professor, however, wanted to be absolutely sure, so he bred rats that received 50,000 IU per day to see whether their offspring would show ill effects. The offspring were fine. So, feeding them the same diet, he let them grow up, breed, and produce their own offspring.
The third generation showed teratological (monster) effects -- predominantly brain damage and hydrocephalus. It is apparent that while loading up on vitamins may seem to be beneficial, such "self-medication" could, in fact, produce changes in the body that could have harmful results years or generations later.
In any case, taking the vitamin A pills available in many stores easily attains 50,000 IU of vitamin A, just tenfold the RDA. Humans have a natural tendency to want more of something that seems to be good for them. (The "If one is good, two is better" mentality.) So it's a natural temptation to megadose on vitamin and mineral pills.
Adapted from The Fit or Fat Target Diet by Covert Bailey. Copyright 1984 by Covert Bailey, published by Houghton Mifflin Company. All rights reserved.