Iron absorption from chewable vitamins with iron versus iron tablets: implications for toxicity

The medical literature contains few, if any, reports of severe iron (Fe) poisonings from ingestion of chewable multivitamins with iron. One possible explanation for this observation is that iron from multivitamins is more poorly absorbed than iron from iron tablets. To compare iron absorption from multivitamins with iron absorption from ferrous fumarate tablets, male adult volunteers were given 6 mg of elemental Fe/kg body weight as chewable multivitamins with iron or as crushed ferrous fumarate tablets in a crossover study. Serum Fe and total iron binding capacity (TIBC) were determined prior to administration of the tablets and one, two, four, and six hours after ingestion. Statistical analyses demonstrated increased and more rapid absorption of Fe from the multivitamin preparation. These results suggest that iron is well absorbed from chewable multivitamins with iron and should theoretically have the potential for producing serious toxicity when taken in overdose. The reasons that such toxicity is not commonly seen clinically are discussed, and a plan for further investigation of this issue is proposed.