Is a 40 % Absorption of Iron from a Ferrous Ascorbate Reference Dose Appropriate to Assess Iron Absorption Independent of Iron Status? Carolina Valenzuela & Manuel Olivares & Alex Brito & Christopher Hamilton-West & Fernando Pizarro Received: 3 May 2013 /Accepted: 14 August 2013 /Published online: 27 August 2013 # Springer Science+Business Media New York 2013 Abstract Although a 40 % absorption of a standard reference dose corresponds to iron (Fe) absorption in borderline Fe- deficient subjects, this percentage is currently applied to all subjects independent of Fe status: (a) to assess the use of the 40 % of Fe absorption of the reference dose (FeRD%) for subjects with iron-depleted stores (IDS), normal Fe status (NIS), Fe deficiency without anemia (IDWA), and Fe defi- ciency anemia (IDA) and (b) to explore relationships between Fe status biomarkers and FeRD%. Six hundred forty-six par- ticipants (582 women and 64 men) were selected from multi- ple Fe bioavailability studies and classified into four groups based on Fe status: NIS, IDS, IDWA, and IDA. All men were classified as normal. The absorption from FeRD% was calcu- lated in each group and correlated with Fe status biomarkers. (a) Women with IDS absorbed 40 (18.9–84.7)% of the refer- ence dose; (b) for male subjects with NIS, the absorption of the reference dose was 19 (9.8–36.1)%, while for females, absorption was observed as to be 34 (16.7–68.6)%. In the case of subjects with IDWA, a 43 (19.7–92.5)% absorption was observed, while subjects with IDA demonstrated 67 (45.2– 98.6)% absorption. Serum ferritin (SF) had the strongest inverse correlation with FeRD% (r = -0.41, p <0.001). A transferrin saturation (TS) <15 % increases the probability that the FeRD% will be highly elevated (OR, 5.05; 95 % CI, 2.73, 9.31; p <0.001). A 40 % absorption as reference dose is only appropriate to assess Fe absorption in subjects with IDS and IDWA. SF had an inverse correlation with FeRD%, and TS increases the probability that the FeRD% will be elevated by over fivefold. Keywords Iron absorption . Reference dose . Ferrous ascorbate . Ferritin . Iron deficiency . Micronutrients Introduction The diets in developing countries typically do not contain enough iron (Fe) to meet nutritional requirements. The popu- lation subgroups especially at risk included infants, young children, and women of childbearing age [1]. Inadequate dietary intake increases the risk of Fe deficiency anemia (IDA), which affects more than one third of the world's population [2]. Fe deficiency (ID) affects these subgroups in different ways. For example, in infants and children, ID im- pairs cognitive development and growth and increases risk of mortality. ID in adulthood lowers physical work capacity and increases risk of mortality in childbirth [3]. Consequently, efforts to improve Fe status are a priority in the realm of public health. Interventions such as Fe supplementation [3], diversi- fication of the diet, and Fe fortification might mitigate the high prevalence of ID. Iron fortification is considered to be the most practical long-term solution for the prevention and con- trol of ID [4]. In order to evaluate the effectiveness of these interventions, assessment of Fe absorption is used as a proxy for bioavailability [3]. Layrisse et al. first established an estimate of 40 % Fe absorption in fasting men [5]. In 1981, Magnusson et al. confirmed the use of this percentage for the absorption of a standard reference dose of 3 mg of Fe as ferrous ascorbate at a 2:1 M ascorbic acid/Fe ratio [6]. Al- though this percentage corresponds to Fe absorption in C. Valenzuela : C. Hamilton-West Faculty of Veterinary and Animal Sciences, University of Chile, Santiago, Chile M. Olivares : A. Brito : F. Pizarro (*) Micronutrients Laboratory, Institute of Nutrition and Food Technology (INTA), University of Chile, Avda El Libano 5524, Casilla 13811, Santiago, Chile e-mail: fpizarro@inta.cl A. Brito United States Department of Agriculture, Western Human Nutrition Research Center, Davis, CA, USA Biol Trace Elem Res (2013) 155:322–326 DOI 10.1007/s12011-013-9797-2