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Getting too little of essential micronutrients can be harmful to your health, especially over the long haul. But getting too much can have equally worrisome
e ects, many of which show up more swi ly. Most troublesome are excesses of fat-soluble vitamins from supplements, which the body may stockpile to the point of reaching toxic doses. e ones most likely to cause trouble are vitamins A, E, and K. (D is also fat-soluble, but an excess of D doesn’t tend to cause problems.)
High doses of supplements—usually from taking individual vitamin and mineral supplements in addi- tion to a powerful multivitamin—are o en at fault. It’s much harder to get dangerous amounts of micronu- trients from food, partly because of the body’s natu- ral checks and balances. When iron stores are full, for example, your body normally absorbs less iron from food unless a genetic disorder or other problem inter- feres. Your body also slows the conversion of beta carotene to vitamin A when it already has enough vitamin A from supplements or food sources. But it is still possible to overdo it.
Many consumers are spurred to take excessive supplement doses by overenthusiastic news stories on the potential bene ts of certain vitamins and miner- als. Remember, though, that the good news from the latest study may be refuted by other studies. Promis- ing test-tube and animal studies o en don’t pan out in people. And certain types of human studies o er more de nitive information than others (see “Making sense of scienti c studies,” page 14). Sometimes, excit- ing results from initial observational studies aren’t con rmed by randomized controlled trials, which are considered the gold standard of research. And even these studies o en have their limitations.
Don’t take more than the recommended dose of any micronutrient through supplements unless there is a good reason to do so, such as speci c advice from your doctor. It is especially important to avoid taking too much of the following vitamins and minerals.