Iron and zinc interactions in humans.

Iron deficiency is the most common nutritional deficiency in the world; zinc deficiency is associated with poor growth and development and impaired immune response. Several Third World countries are taking measures to increase the dietary intake of iron and zinc with fortification of foods or dietary supplements. Several studies showed that high iron concentrations can negatively affect zinc absorption in adults when these trace minerals are given in solution. However, when iron and zinc are given in a meal, this effect is not observed. Solomons (J Nutr 1986;116:927-35) postulated that the total amount of ionic species affects the absorption of zinc and that a total dose of >25 mg Fe may produce a measurable effect on zinc absorption. This could occur if iron supplements are taken with a meal, and iron experts recommend that iron supplements be taken between meals. Recent studies using stable isotopes showed that fortifying foods with iron at current fortification amounts has no adverse effect on zinc absorption. There are 5 zinc salts listed as generally recommended as safe (GRAS) by the US Food and Drug Administration for food fortification. From 1970 to 1987, the total amount of zinc salts used in food continually increased, with zinc oxide and zinc sulfate showing the largest increases. Twelve iron sources are listed as GRAS; elemental iron has become the source of choice because it is less expensive to produce and has fewer organoleptic problems. Use of ferrous fumarate is also increasing.