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Body iron excretion by healthy men and women^1,2,3,4

¹ From the US Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND (JRH, CAZ, and LKJ), and the University of North Dakota, Grand Forks, ND (LKJ).

² Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.

³ Supported by the USDA Agricultural Research Service.

⁴ Address correspondence to JR Hunt, US Department of Agriculture, ARS, GFHNRC, 2420 2nd Avenue N, Stop 9034, Grand Forks, ND 58202-9034. E-mail: janetrhunt{at}gmail.com.

Background: Iron excretion measured by isotope dilution has been a primary basis for the factorial derivation of recommendations for iron intake, but the results have been available for men only.

Objective: The objective of this study was to confirm iron excretion measurements in healthy men and extend them to women.

Design: The turnover rate of ⁵⁵Fe that had been administered 1 y earlier was determined from blood sampled semiannually for up to 3 y from 53 subjects in the community. Body iron was determined from hemoglobin, serum ferritin, and transferrin receptor. Complete menstrual collections were obtained from 13 women.

Results: The total median (range) iron excretion was 1.18 (0.11–2.07) mg/d for 29 men, 1.58 (0.65–4.88) mg/d for 19 menstruating women, and 0.99 (0.86–1.57) for 5 postmenopausal women. When hormonal contraceptive users were omitted, the median for 15 menstruating women increased to 1.66 mg/d. The distribution of iron excretion was normal for the men and postmenopausal women and was highly skewed for the menstruating women; menstrual iron accounted for 90% of the variation. Iron excretion was not strongly related to body weight. Body iron in menstruating women decreased somewhat (by 4.6%) in the men and tended to increase (by 1.5%) during the study.

Conclusions: The results extend direct iron excretion measurements in men to include similar measurements in women. The results emphasize the wide range of iron excretion in humans, which results in a 40-fold range of requirements for absorbed iron. This trial was registered at clinicaltrials.gov as NCT00755105.