Dietary Intakes Based on food Composition Data May underestimate Contribution of Potentially Exchangeable Contaminant Iron from Soil

Abstract

Objectives: Soil-iron contaminant has the potential to contribute to total iron intakes, depending in part on food preparation practices, although whether contaminant iron joins the common non-heme iron pool and is available for absorption is uncertain. Therefore we compared dietary Iron intakes analyzed from diet composites with those calculated from food composition data and examined them in relation to iron biomarkers, adjusted for inflammation. Methods: Weighed duplicate diet composites, diet records, and fasting blood samples were collected on the same day from a convenience sample of women aged 18 to 50 y from Zombwe in Mzimba (n=60) and Mikalango in Chikhwawa (n= 60) in rural Malawi. Diet composites were analyzed by ICP-MS, and blood for hemoglobin, ferritin, transferrin receptor, and inflammatory biomarkers. Results: Median analyzed iron intakes (mg/d) were higher than calculated intakes in Zombwe (16.6 vs. 10.1; p<0.001) and Mikalango (29.6 vs. 19.1; p<0.001) and accompanied by high levels of Al and Ti, markers of soil contamination. Less than 15% of women had storage iron depletion (ferritin 12 µg/L and haemoglobin >120 g/L) or iron deficiency (total body Fe<0 mg/kg), despite negligible intakes of readily absorbable heme iron and high phytate intakes in both districts. Conclusions: Assessment of iron intakes from food composition data where soil contaminant iron is likely yielded an underestimate of total iron intake. Some contaminant iron may be exchangeable and available for absorption, depending on soil mineralogy. In such settings, collection and chemical analysis of weighed duplicate diet composites are preferable for assessing total iron intakes.