Iron absorption in man - diet modification and fortification

Abstract

Background: Iron (Fe) deficiency is globally the most common form of nutrient deficiency. The approach to combat this problem can be divided into two major strategies a): increasing the dietary Fe bioavailability by diet modification, or b): increasing the Fe intake through fortification. However, human bioavailability data on the most commonly used form of Fe fortificants, elemental Fe powders (Feelem), are limited. The main reason is the lack of methods for measuring absorption from Feelem. Furthermore, when it comes to the scientific evidence for the comparative effect from each of these two strategies in improving Fe uptake in man, there are still questions.

Aims: To I): evolve a method which could be used to characterize the relative bioavailability (RBV) of Feelem II): characterize the RBV of Feelem fortificants, and finally III): study the effect from dietary modifications and/or Fe fortification on Fe absorption and rates of changes in Fe stores.

Methods: To address the given aims the following methods were used in human subjects; Extrinsic labeling with radioactive Fe isotopes and whole-body counting; The area under the serum Fe concentration curve during six hours following administration of 100 mg Fe (S-Fe AUC0-6h). Algorithms based on human data were used as well.

Results: Radioiron absorption and S-Fe AUC0-6h correlated well (r2=0.94). The studied Feelem were all significantly less well absorbed relative ferrous sulfate (RBV=36-65%). Adding 20 g meat, or 20 g meat and 20 mg ascorbic acid to a meal with low Fe bioavailability increased the total Fe absorption with 155% and 227%, respectively. Improvements in Fe status were greater after dietary modifications than after Fe fortification for a diet with low Fe bioavailability.

Main conclusions: S-Fe AUC0-6h following oral administration of 100 mg Fe is a valid measure of Fe absorption. Dietary modifications of meals with low Fe bioavailability can markedly improve Fe absorption, especially when adding meat which also contributes with highly absorbable heme Fe. Depending on choice of Feelem in fortification programs effectiveness can differ. Further, if the diet has a low Fe bioavailability, it is difficult to achieve good effects on Fe status by using Fe fortification as the only measure. Thus, the overall conclusion of this thesis is that the best course of action for interventions designed to improve Fe status, firstly must be to ensure an adequate dietary Fe bioavailability, and secondly to use a Fe fortificant with high bioavailability.