Quantitative relations between baseline iron status , study duration , and iron dose on changes in iron-status biomarkers , which were generated from the meta-analyses , can be used to predict effects of trials of iron supplementation and fortification and to design iron-intervention programs
BACKGROUND The response of status biomarkers to an increase in iron supply depends on several physiologic and environmental factors , which make it difficult to predict the outcome of an intervention .
OBJECTIVE We assessed effects of baseline iron status , sex , menopausal status , duration of intervention , iron form , and daily dose on the change in iron status in response to iron supplementation .
Adaptation in iron absorption: iron supplementation reduces nonheme-iron but not heme-iron absorption from food.
BACKGROUND Results of cross-sectional studies suggest that in healthy people , iron absorption adapts to meet physiologic needs and stabilize iron stores , but this has not been adequately tested in longitudinal studies . OBJECTIVE We tested whether heme- and nonheme-iron absorption decrease in response to increased iron intake and whether iron stores reach a steady state . DESIGN In a r and omized , placebo-controlled trial , heme- and nonheme-iron absorption by healthy men and women ( n = 57 ) were measured before and after 12 wk of supplementation with 50 mg Fe/d as ferrous sulfate .  Serum and fecal ferritin were measured during supplementation and for 6 mo thereafter . RESULTS Initially , both heme- and nonheme-iron absorption were inversely associated with serum ferritin concentration .  Volunteers who took iron supplements  , even those with serum ferritin < 21 microg/L ( n = 5 ) , adapted to absorb less nonheme iron ( 3.2 % at week 12 compared with 5.0 % at week 0 , P : < 0.001 ) but not less heme iron from a beef-based meal . Serum ferritin concentration was slightly but significantly higher after iron supplementation than after placebo ( difference = 13 microg/L ) . This higher ferritin concentration persisted for > /=6 mo after supplementation , except in subjects with low iron stores , whose serum ferritin returned to baseline within 3 mo . Fecal ferritin excretion increased 2.5-fold ( P : < 0.05 ) during supplementation . CONCLUSIONS Healthy individuals , even those with low iron stores , had reduced nonheme-iron absorption from food in response to iron supplementation . Despite this partial adaptation , iron stores were greater after iron supplementation than after placebo and this difference was sustained , except in individuals with the lowest iron stores
Quantitative relations between baseline iron status , study duration , and iron dose on changes in iron-status biomarkers , which were generated from the meta-analyses , can be used to predict effects of trials of iron supplementation and fortification and to design iron-intervention programs
BACKGROUND The response of status biomarkers to an increase in iron supply depends on several physiologic and environmental factors , which make it difficult to predict the outcome of an intervention .
OBJECTIVE We assessed effects of baseline iron status , sex , menopausal status , duration of intervention , iron form , and daily dose on the change in iron status in response to iron supplementation .