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United States Department of Agriculture

Agricultural Research Service

Research Project: KNOWLEDGE OF SOIL-PLANT-HUMAN FOOD SYSTEMS TO ENHANCE IRON AND ZINC BIOAVAILABILITY IN PLANT FOODS

Location: Plant, Soil and Nutrition Research

Title: Bioavailability of iron in geophagic earths and clay minerals, and their effect on dietary iron absorption using an in vitro digestion/Caco-2 cell model

Authors
item Seim, Gretchen -
item Ahn, Cedric -
item Bodis, Mary -
item Luwedde, Flavia -
item Miller, Dennis -
item Hillier, Stephen -
item Tako, Elad
item Glahn, Raymond
item Young, Sera -

Submitted to: Food and Function
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 12, 2013
Publication Date: July 1, 2013
Repository URL: http://DOI: 10.139/c3f03030b
Citation: Seim, G., Ahn, C.I., Bodis, M., Luwedde, F., Miller, D., Hillier, S., Tako, E.N., Glahn, R.P., Young, S.L. 2013. Bioavailability of iron in geophagic earths and clay minerals, and their effect on dietary iron absorption using an in vitro digestion/Caco-2 cell model. Food and Function. 4(8):1263-1270.

Interpretive Summary: Geophagy, the intentional ingestion of earth, is practiced in many cultures on all inhabited continents. Despite its recognition as a behavior with public health implications, the cause and consequences of geophagy remain unclear. Geophagy is frequently associated with anemia, especially iron deficiency anemia. Therefore it has been proposed that geophagy may be practiced as a means to improve iron status by providing iron to its consumers. Conversely it has also been proposed that geophagy may instead cause iron deficiency by inhibiting the body’s absorption of iron from other sources. Using an in vitro digestion cell model that measures iron bioavailability we tested these hypotheses. To test the first hypothesis, 12 samples of geophagic earth and 4 samples of pure clay minerals were brought through simulated digestion and resulting bioavailable iron was measured. It was found that despite high levels of elemental iron in these samples, very little of this iron was bioavailable. We used this same model to test the second hypothesis; the earth and clay samples were combined with iron-rich white bean and then brought through simulated digestion. By measuring the resulting bioavailable iron we could assess if the addition of earth or clay caused a reduction in the bioavailablity of iron from white beans. Some (but not all) of the samples were found to have the ability to inhibit iron absorption from a food source.

Technical Abstract: Geophagy, the deliberate consumption of earth, is strongly associated with iron (Fe) deficiency. It has been proposed that geophagy may be practiced as a means to improve Fe status by increasing Fe intakes and, conversely, that geophagy may cause Fe deficiency by inhibiting Fe absorption. We tested these hypotheses by measuring Fe concentration and relative bioavailable Fe content of 12 samples of geophagic earth and 4 samples of pure clay minerals. Further, we assessed the impact of these samples on the bioavailability of Fe from an Fe-rich test meal (cooked white beans, WB). Fe concentrations were measured with inductively coupled plasma atomic emission spectroscopy. Fe bioavailability was determined using an in vitro digestion/Caco-2 cell model in which ferritin formation was used as an index of Fe bioavailability. Geophagic earth and clay mineral samples were evaluated with this model, both alone and in combination with WB (1:16 ratio, sample:WB). Median Fe concentration of the geophagic earth was 3485 (IQR 2462, 14571) ug/g and mean Fe concentration in the clay minerals was 2791 (+/- 1782) µg/g. All specimens had Fe concentrations significantly higher (p = 0.005) than the Fe concentration of WB (77 ug/g). Ferritin formation (i.e. Fe uptake) in cells exposed to geophagic earths and clay minerals was significantly lower than in cells exposed to WB (p = 0.05) and Fe uptake responses of 11 of the 16 samples were not significantly different from the blank, indicating no bioavailable Fe. When samples were combined with WB, 5 of 16 had mean ferritin levels that were significantly lower (p = 0.05, one tail) than the WB alone, indicating that the samples inhibited Fe uptake from the WB. None of the ferritin responses of cells exposed to both WB and earth/clay were significantly higher than WB alone. Thus, although geophagic earths and mineral clays are high in total Fe, very little of this Fe is bioavailable. Further, some geophagic earth and clay mineral samples inhibit Fe absorption from foods. In vivo research is warranted to confirm these observations and to determine if geophagic earth samples can be a source of Fe and/or inhibit Fe absorption.

Last Modified: 9/20/2014