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Wed, 25 Jan 2006

Vitamin A poisoning

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In an earlier post I remarked that "The liver of arctic animals . . . has a toxically high concentration of vitamin D". Dennis Taylor has pointed out that this is mistaken; I meant to say "vitamin A". Thanks, Dennis.

B and C vitamins are not toxic in large doses; they are water-soluble so that excess quantities are easily excreted. Vitamins A and D are not water-soluble, so excess quantities are harder to get rid of. Apparently, though, the liver is capable of storing very large quantities of vitamin D, so that vitamin D poisoning is extremely rare.

The only cases of vitamin A poisoning I've heard of concerned either people who ate the livers of polar bears, walruses, sled dogs, or other arctic animals, or else health food nuts who consumed enormous quantities of pure vitamin A in a misguided effort to prove how healthy it is. In On Food and Cooking, Harold McGee writes:

In the space of 10 days in February of 1974, an English health food enthusiast named Basil Brown took about 10,000 times the recommended requirement of vitamin A, and drank about 10 gallons of carrot juice, whose pigment is a precursor of vitamin A. At the end of those ten days, he was dead of severe liver damage. His skin was bright yellow.

(First edition, p. 536.)

There was a period in my life in which I was eating very large quantities of carrots. (Not for any policy reason; just because I like carrots.) I started to worry that I might hurt myself, so I did a little research. The carrots themselves don't contain vitamin A; they contain beta-carotene, which the body converts internally to vitamin A. The beta-carotene itself is harmless, and excess is easily eliminated. So eat all the carrots you want! You might turn orange, but it probably won't kill you.


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