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Nutrient Requirements

Inevitable Iron Loss by Human Adolescents, with Calculations of the Requirement for Absorbed Iron¹

Department of Pediatrics, University of Iowa, Iowa City, IA and ^* Department of Preventive Medicine and Community Health, University of Texas Medical Branch, Galveston, TX

²To whom correspondence should be addressed. E-mail: samfomon{at}aol.com.

In growing individuals, the requirement for absorbed iron consists of iron needed for growth and iron needed to replace inevitable iron loss. We were able to estimate inevitable iron loss by adolescents because total body iron of the adolescents had been enriched with the stable isotope, ⁵⁸Fe, as the result of earlier studies of iron absorption. During an interval beginning at least 1.56 y after isotope administration (a time sufficient for complete mixing of the isotope with total body iron) and extending for no less than 3.29 y, we determined the isotopic enrichment of circulating iron. On the basis of several assumptions, we calculated total body ⁵⁸Fe and total body iron at the beginning and end of the interval. Because of complete mixing of the isotope with total body iron, fractional total ⁵⁸Fe loss was the same as fractional loss of total iron. In males, the fractional loss of iron was 9.70%/y and the quantitative loss was 256 mg/y or 0.70 mg/d. In females, the fractional loss of iron was 14.60%/y and the quantitative loss was 306 mg/y or 0.84 mg/d. Using several assumptions, we then calculated that the iron requirement for growth during this interval was 0.76 mg/d for males and 0.31 mg/d for females. Adding the iron loss to the iron requirement for growth, the requirement for absorbed iron was estimated to be 1.46 mg/d for males and 1.15 mg/d for females.

KEY WORDS: • iron loss • iron requirements • stable isotopes • adolescents

This article has been cited by other articles:

				S. J. Fomon, S. E. Nelson, R. E. Serfass, and E. E. Ziegler Absorption and Loss of Iron in Toddlers Are Highly Correlated J. Nutr., April 1, 2005; 135(4): 771 - 777. [Abstract] [Full Text] [PDF]