There are two nutrients commonly found in multivitamins formulations that do warrant a note of caution because of their potential for cumulative toxicity. Long-term intakes of high levels of vitamin A and iron have been associated with toxicity implications.
Ingestion of too much vitamin A can be toxic, particularly if there are defects in liver function. In pregnancy, dosages greater than 10,000 IU of vitamin A have been shown to cause birth defects, particularly during the first seven weeks after conception. Women who may becomes pregnant should limit their supplemental vitamin A intake to below 5,000 IU, or preferably supplement with beta-carotene
Iron at high dosages becomes a potent oxidant and free radical generator that can accelerate oxidative damage of cholesterol with the consequent onset of arteriosclerosis.
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