ARS | Publication request: Absorption of Nonheme, But Not Heme Iron, Is Substantially Reduced with High Iron Stores

Submitted to: American Dietetic Association Annual Meeting
Publication Type: Abstract
Publication Acceptance Date: April 1, 2006
Publication Date: August 1, 2006
Citation: Hunt, J.R. 2006. Absorption of nonheme, but not heme iron, is substantially reduced with high iron stores [abstract]. Journal of the American Dietetic Association. 106(8)S2:A-42.

Technical Abstract: Humans absorb heme iron from meat, poultry and fish more efficiently than nonheme iron, and high consumption may increase body iron stores, and possibly oxidative stress. Results from previous studies of heme and nonheme iron bioavailability, measured separately for men and for women, were combined to model the relative absorption of each form of iron in relation to body iron stores. Iron absorption was measured in healthy men (n=14) and premenopausal women (n=18) consuming controlled, high bioavailability diets. Adjusted for individual energy intake, the diets provided 10-14 oz/d of meat or poultry, refined grains and cereal products, no coffee or tea, and greater than or equal to 75 mg ascorbic acid with each meal. By analysis, the diet contained 12.9 mg iron/2500 kcal, with 1.4 mg or 11% as heme iron. Iron absorption was measured by radiolabeling the 2-d menu with 59FeCl3 and 55Fe hemoglobin, and measuring whole body and erythrocyte retention after 2 wk. With all variables logarithmically transformed, total iron absorption (0.4 to 4.5 mg/d) and nonheme iron absorption, but not heme iron absorption, were inversely related to serum ferritin (4 to 308 micro g/L) (R2 = 0.66, p<0.01). Subjects with the lowest iron stores absorbed iron mostly in the nonheme form, and heme iron accounted for 15-20% of the iron absorbed. With higher iron stores, nonheme iron absorption decreased, with the result that heme iron accounted for half of the iron absorbed by subjects with serum ferritin greater than or equal to 150 micro g/L. Unlike nonheme iron, heme iron absorption is not substantially reduced as iron stores increase.