Int. J. Vitam. Nutr. Res. 80 (4 – 5), 2010, 307 – 313 307 DOI 10.1024/0300-9831/a000038 Int. J. Vitam. Nutr. Res. 80 (4 – 5) © 2010 Hans Huber Publishers, Hogrefe AG, Bern Article to the Special Issue The Use of Caco-2 Cells to Estimate Fe Absorption in Humans – a Critical Appraisal Ann-Sofie Sandberg Chalmers University of Technology, Department of Chemical and Biological Engineering, Food Science, Gothenburg, Sweden Abstract: The Caco-2 cell model is widely used to assess the bioaccessibility/availability of iron from foods and diets. Analysis of iron uptake in this human epithelial cell line is usually preceded by a two- step digestion to simulate the conditions in the stomach and small intestine. Moreover, culturing the cells on inserts permits the measurement of iron transport. The cellular iron uptake is determined by direct measurements using radioisotopes, or indirectly by measurement of ferritin, the intracellular storage form of iron. There is a good correlation between Caco-2 cell uptake and human iron bioavailability for a number of dietary factors known to affect iron absorption. However, recent data suggest that in some cases there is no correlation. Possible reasons for such discrepancies, the benefits, and limitations of the Caco-2 cell model are discussed. In conclusion, in vitro experiments with Caco-2 cells are impor- tant tools for ranking foods with respect to bioavailability, for mechanistic studies of iron absorption, and for studies of dietary factors influencing absorption. The results need to be confirmed in humans. Key words: Caco-2 cells, iron bioavailability, in vitro digestion Introduction Low bioavailability of iron is a major nutritional prob- lem in developing countries, where the diet is based on staple foods. One strategy to improve the iron status is to biofortify staple food crops with iron and other micronutrients. For this reason, to rank the foods with respect to iron bioavailability, there is a need for a sim- ple method to estimate iron bioavailability in humans. Such a method must be reproducible and reflect the in vivo conditions. It is thus of great importance that the in vitro methods are validated by in vivo measure- ments in humans. Traditionally a combined two step in vitro digestion and measurement of dialyzable or soluble iron is used to determine iron availability [1]; i. e. , iron that is potentially available for absorption in the gut. Dialyzability methods are useful for screening purposes to identify major differences in availability, but it cannot predict the magnitude of response [2, 3]. For example, methods based on dialyzability exclude iron that is bound to large but not small molecules. However, some of these iron-bound large molecule complexes (e. g., ferritin) have substantial bioavail- ability whereas iron bound to certain small molecules is not bioavailable [4]. Combining in vitro digestion with uptake in Caco-2 cells is a step forward since it predicts both availabil- ity and uptake into the enterocyte and at times also the absorption. However, in a consensus statement of experts working in the field of iron nutrition, it was