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ARS Home » Plains Area » Grand Forks, North Dakota » Grand Forks Human Nutrition Research Center » Healthy Body Weight Research » Research » Publications at this Location » Publication #109356
Title: ADAPTATION IN IRON ABSORPTION: IRON SUPPLEMENTATION REDUCES NONHEME, BUT NOT HEME IRON ABSORPTION FROM FOOD

Author
item Roughead, Zamzam
item Hunt, Janet

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2000
Publication Date: 10/1/2000
Citation: Roughead, Z.K., Hunt, J.R. 2000. Adaptation in iron absorption: Iron supplementation reduces nonheme, but not heme iron absorption from food. American Journal of Clinical Nutrition. 72:982-989.

Interpretive Summary: People are consuming more iron in the US because of increased fortification of foods and use of nutrient supplements. To help understand how well the body adapts to changes in iron intake, we investigated how well men and women adapted to supplementation with 50 mg iron daily for 12 weeks. Those supplemented with iron, rather than a placebo, adapted to reduce the amount of iron they absorbed from food (a meal of hamburger, French fries, and milkshake) by about 25%. This reduction occurred for nonheme iron, the form of iron found in most foods and in iron supplements, but not for heme iron, a form of iron supplied by meat, poultry, and fish. Iron supplements increased body iron stores, and iron stores remained greater for at least 6 months after supplementation in the men and women with adequate to high iron stores, but not in those with low iron stores. These results indicate that people with adequate iron stores do not fully adapt to prevent increased iron stores with supplementation, but that women with low iron stores may need continuing iron supplementation or other dietary interventions to counterbalance high rates of iron excretion.

Technical Abstract: Background: Cross-sectional studies suggest that healthy people adapt their iron absorption to meet physiological needs and to stabilize iron stores, but this has not been adequately tested in longitudinal studies. Objective: To test whether people a) adapt to decrease their heme and nonheme iron absorption with increased iron intake, and b) reach a steady- state in their iron stores, as indicated by serum ferritin. Design: In a randomized, placebo-controlled trial, heme and nonheme iron absorption by healthy men and women (n = 57) were measured before and after 12 wk of daily supplementation with 50 mg of iron as ferrous sulfate. Serum and fecal ferritin were measured during and for 6 mo after supplementation. Results: Initially, both heme and nonheme iron absorption were inversely associated with serum ferritin. Volunteers supplemented with iron, even those with serum ferritin <21 ug/L (n = 5), adapted to absorb less nonheme (5.0% at wk 0 vs. 3.2% at wk 12, p<0.001), but not heme iron from a beef- based meal. A slightly, but significantly greater serum ferritin (13 ug/L more than placebo) persisted for at least 6 mo after supplementation, except in those with low iron stores, whose serum ferritin returned to baseline within 3 mo. Fecal ferritin excretion increased by 2.5 fold (p<0.05) during supplementation. Conclusions: Healthy individuals, even those with low iron stores, reduced nonheme iron absorption from food in response to iron supplementation. Despite this partial adaptation, iron stores were greater after iron supplementation and this difference was sustained except in those with the lowest iron stores.