Dietary iron bioavailability in premenopausal Australian women

Iron deficiency is the most common nutritional deficiency globally. Premenopausal women are at particular risk due to increased requirements for iron associated with menstrual blood loss and pregnancy. To prevent iron deficiency, recommended intakes have been developed based on physiological requirements for absorbed iron and iron bioavailability. However, iron bioavailability is difficult to estimate as it depends on the composition of the diet and an individual’s absorptive efficiency. Several algorithms have been proposed to estimate iron bioavailability from diets based on the form of the iron and the presence of absorption modifiers. These algorithms can be complex and often underestimate bioavailability. Recently, a new approach was developed by Dainty et al.(1,2), which is based on calculated iron requirements, total dietary iron intakes, and the distribution of serum ferritin concentration values in the population. This model has been used by the European Food Safety Authority to set recommended iron intakes for adults(3). In contrast, the recommended iron intakes for Australian adults are based on iron bioavailability estimates from the US Institute of Medicine, which were primarily derived from 15 free living US adults(4). Therefore, the aim of this study was to predict dietary iron absorption in a representative sample of premenopausal Australian women using the model developed by Dainty et al.(1,2) Dietary iron intake and serum ferritin data from the 2011–13 Australian National Nutrition and Physical Activity Survey and National Health Measures Survey were analysed in 503 premenopausal women aged 18–49 years. Women were excluded if they were pregnant or lactating, had elevated C-reactive protein, consumed iron-containing supplements, or misreported energy intake. Dietary iron intake was assessed via two non-consecutive 24-hour recalls. Usual daily iron intake was determined by the Multiple Source Method. Dietary iron absorption was estimated using the predictive model developed by Dainty et al.(1,2) and the Institute of Medicine’s distribution of individual dietary iron requirements(4). Mean (SD) usual dietary iron intake was 10.4 (2.6) mg/d. The prevalence of serum ferritin < 15 μg/L was 14.1% (95% CI: 10.2%, 19.3%), and < 30 μg/L was 37.0% (95% CI: 31.8%, 42.5%). Predicted dietary iron absorption at serum ferritin concentrations of < 15 μg/L was 29.5%, and at serum ferritin concentrations of < 30 μg/L it was 19%. Our findings do not support the bioavailability assumption of 18% used to develop the Australian recommended iron intakes for premenopausal women based on the need to maintain serum ferritin concentrations of 15 μg/L. Our results may be useful in revising the recommended iron intakes for Australian premenopausal women.