Measurement of long‐term iron absorption and loss during iron supplementation using a stable isotope of iron (⁵⁷Fe)

Abstract

We report the first measurements of long-term iron absorption and loss during iron supplementation in African children using a stable isotope of iron (⁵⁷ Fe). After uniform labelling of body iron with ⁵⁷ Fe, iron absorption is proportional to the rate of decrease in the ⁵⁷ Fe tracer concentration, while iron loss is proportional to the rate of decrease in the ⁵⁷ Fe tracer amount. Anaemic Gambian toddlers were given 2 mg ⁵⁷ Fe orally to equilibrate with total body iron over 8-11 months. After assignment to the positive control arm of the HIGH study, 22 toddlers consumed a micronutrient powder containing 12 mg iron for 12 weeks followed by 12 weeks without iron supplementation. Their daily iron absorption increased 3·8-fold during the iron supplementation period compared to the control period [median (interquartile range, IQR): 1·00 (0·82; 1·28) mg/day vs. 0·26 (0·22; 0·35) mg/day; P = 0·001]. Unexpectedly, during the supplementation period, daily iron loss also increased by 3·4-fold [0·75 (0·55; 0·87) mg/day vs. 0·22 (0·19; 0·29) mg/day; P = 0·005]. Consequently, most (~72%) of the absorbed iron was lost during supplementation. Long-term studies of iron absorption and loss are a promising and accurate method for assessing and quantifying long-term iron balance and may provide a reference method for evaluating iron intervention programs in vulnerable population groups. This study was registered as ISRCTN 0720906.