Modeling tool for calculating dietary iron bioavailability in iron-sufficient adults

Abstract

Background: Values for dietary iron bioavailability are required for setting dietary reference values. These are estimated from predictive algorithms, nonheme iron absorption from meals, and models of iron intake, serum ferritin concentration, and iron requirements.Objective: We developed a new interactive tool to predict dietary iron bioavailability.Design: Iron intake and serum ferritin, a quantitative marker of body iron stores, from 2 nationally representative studies of adults in the United Kingdom and Ireland and a trial in elderly people in Norfolk, United Kingdom, were used to develop a model to predict dietary iron absorption at different serum ferritin concentrations. Individuals who had raised inflammatory markers or were taking iron-containing supplements were excluded.Results: Mean iron intakes were 13.6, 10.3, and 10.9 mg/d and mean serum ferritin concentrations were 140.7, 49.4, and 96.7 mg/L in men, premenopausal women, and postmenopausal women, respectively. The model predicted that at serum ferritin concentrations of 15, 30, and 60 mg/L, mean dietary iron absorption would be 22.3%, 16.3%, and 11.6%, respectively, in men; 27.2%, 17.2%, and 10.6%, respectively, in premenopausal women; and 18.4%, 12.7%, and 10.5%, respectively, in postmenopausal women.Conclusions: An interactive program for calculating dietary iron absorption at any concentration of serum ferritin is presented. Differences in iron status are partly explained by age but also by diet, with meat being a key determinant. The effect of the diet is more marked at lower serum ferritin concentrations. The model can be applied to any adult population in whom representative, good-quality data on iron intake and iron status have been collected. Values for dietary iron bioavailability can be derived for any target concentration of serum ferritin, thereby giving risk managers and public health professionals a flexible and transparent basis on which to base their dietary recommendations. This trial was registered at clinicaltrials.gov as NCT01754012.

Keywords: bioavailability model; dietary iron absorption; dietary iron intake; dietary reference values; iron; iron bioavailability; iron intake; serum ferritin.

© 2017 American Society for Nutrition.

Figures

FIGURE 1

Cumulative distribution (percentage of participants in each group) of serum ferritin concentrations for men, premenopausal women, and postmenopausal women by study. The number of participants were as follows—men: black bars, n = 336; gray bars, n = 494; and white bars, n = 77; premenopausal women: black bars, n = 197; and gray bars, n = 363; and postmenopausal women: black bars, n = 117; gray bars, n = 158; and white bars, n = 119. Mean ± SD serum ferritin values were 140.7 ± 113.6, 49.4 ± 45.8, and 96.7 ± 72.8 μg/L in men, premenopausal women, and postmenopausal women, respectively. NANS, National Adult Nutrition Survey; NDNS, National Diet and Nutrition Survey; NU-AGE, New Dietary Strategies Addressing the Specific Needs of Elderly Population for a Healthy Ageing in Europe.

FIGURE 2

Predicted prevalence (percentage) of inadequate iron intakes at different iron absorptions in men, premenopausal women, and postmenopausal women. Dietary absorption values ranged from 0% to 40%.

FIGURE 3

Percentage of estimated dietary iron absorption for selected serum ferritin values for men, premenopausal women, and postmenopausal women. Serum ferritin concentrations ranged from

FIGURE 4

Adjusted mean ± SE serum ferritin concentrations by Q of iron intake from meat stratified by sex and adjusted for age (years), BMI (in kg/m2), total iron intake (milligrams per day), and study cohort. Mean ± SD iron intakes from meat in each Q were as follows; women: 1, 0.2 ± 0.2 mg/d; 2, 0.8 ± 0.1 mg/d; 3, 1.3 ± 0.1 mg/d; 4, 1.9 ± 0.2 mg/d; and 5, 3.2 ± 1.2 mg/d; men, 1, 0.6 ± 0.3 mg/d; 2, 1.5 ± 0.2 mg/d; 3, 2.3 ± 0.2 mg/d; 4, 3.1 ± 0.3 mg/d; and 5, 5.0 ± 1.5 mg/d. P-trend values were calculated with the use of an ANCOVA. Q, quintile.