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Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc
Recommended Iron Intake
Iron bioavailability is reduced in vegetarian diets, both because of the absence of easily absorbed heme iron and because of the presence of inhibitors of iron absorption. The percent bioavailability was estimated at 10 percent (versus 18 percent in omnivorous diets). Thus, the iron requirement for vegetarians would be approximately 1.8 times higher than the values established for omnivores, and recommended intakes could be adjusted using a similar factor.
Basal losses of iron by athletes performing intense exercise on a daily basis are elevated, with estimates ranging from a 30 to 70 percent increase. Therefore, the iron requirement is increased for those who exercise intensely on a daily basis. It should be noted, however, that much of the research conducted with respect to iron needs of athletes has been done with runners. The postulated mechanisms of increased basal losses (hematuria and fecal blood loss) may not occur to as great an extent in athletes who participate in other sports.
The donation of 1 unit of blood/year is estimated to increase the need for absorbed iron by 0.6 to 0.7 mg/day, which, assuming 18 percent absorption, suggests that intake would need to be 3 to 4 mg/ day higher. Thus, individuals who donate blood on a regular basis will have an increased iron requirement. Presumably, iron needs of frequent donors would increase in proportion to the amount of blood donated.
of the average requirement of individuals consuming diets with low zinc bioavailability cannot be made at this time. However, it seems reasonable to suggest that such individuals should be counseled to consume intakes that are at least equal to the RDA, and perhaps up to as much as twice the RDA.
The Tolerable Upper Intake Level (UL) for zinc for adults is 40 mg, which exceeds the RDA for men by somewhat less than four-fold and for women by five-fold. Although intakes of zinc above 40 mg/day from food alone are uncommon (the ninety-ninth percen-