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United States Department of Agriculture

Agricultural Research Service

Title: Iron Excretion of Healthy Men and Women, Measured by Isotope Dilution

Authors
item Hunt, Janet
item Johnson, Luann - UNIV OF NORTH DAKOTA

Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: November 10, 2005
Publication Date: March 6, 2006
Citation: Hunt, J.R., Johnson, L.K. 2006. Iron excretion of healthy men and women, measured by isotope dilution [abstract]. FASEB J. 20(4):A194.

Technical Abstract: Iron (Fe) excretion measurements, conducted principally with men (Green et. al., 1968), have been applied to derive factorial estimations of dietary Fe requirements. To expand such measurements to healthy women, and to test the hypothesis that Fe excretion of men is proportional to body Fe stores, Fe excretion was determined by isotope dilution. Healthy men and women in Fe absorption studies had consumed 55Fe (emits low-energy X-rays; 2.7 y physical half-life) at least 1 y earlier, allowing tracer equilibration in body Fe pools. They did not use Fe supplements or donate blood. Blood (30 mL) collected every 6-mo for 3 yr was analyzed for 55Fe in a single batch per volunteer. Biological half-lives were determined from semi-logarithmic retention curves, and blood and body Fe were estimated from hemoglobin and serum transferrin receptor/ferritin ratio (Cook, 2003), respectively. Menstruating women (n=19) excreted 1.5 mg Fe/d (geometric mean), with a skewed distribution from 0.6 to 4.3. This increased to 1.7 when 4 users of hormonal contraceptives were eliminated. Men (n=29) excreted 0.8 (0.1 to 1.9) mg Fe/d, not significantly skewed (0.97±0.42 without ln transformation). Post-menopausal women (n=5) excreted 0.9 (0.8 to1.4) mg Fe/d. Fe excretion was inversely associated with serum ferritin in menstruating women (R2 = 0.34, p<0.01), but not in men (R2=0.003, NS). Fe excretion correlated strongly with chemical analyses of menstrual Fe (R2=0.88, n=14), but was not associated with body weight or frequency of exercise in either gender. Fe excretion measurements in women can contribute to dietary recommendations without extrapolation from results with men.

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