In overweight and obese women, dietary iron absorption is reduced and the enhancement of iron absorption by ascorbic acid is one-half that in normal-weight women.

BACKGROUND: Iron deficiency is common in overweight and obese individuals. This deficiency may be due to adiposity-related inflammation that increases serum hepcidin and decreases dietary iron absorption. Because hepcidin reduces iron efflux from the basolateral enterocyte, it is uncertain whether luminal enhancers of dietary iron absorption such as ascorbic acid can be effective in overweight and obese individuals.

OBJECTIVE: In this study, we compared iron absorption from a meal with ascorbic acid (+AA) and a meal without ascorbic acid (-AA) in women in a normal-weight group (NW) with those in overweight and obese groups combined (OW/OB).

DESIGN: Healthy, nonanemic women [n = 62; BMI (in kg/m(2)): 18.5-39.9] consumed a stable-isotope-labeled wheat-based test meal -AA and a wheat-based test meal +AA (31.4 mg ascorbic acid). We measured iron absorption and body composition with the use of dual-energy X-ray absorptiometry, blood volume with the use of a carbon monoxide (CO)-rebreathing method, iron status, inflammation, and serum hepcidin.

RESULTS: Inflammatory biomarkers (all P < 0.05) and hepcidin (P = 0.08) were lower in the NW than in the OW/OB. Geometric mean (95% CI) iron absorptions in the NW and OW/OB were 19.0% (15.2%, 23.5%) and 12.9% (9.7%, 16.9%) (P = 0.049), respectively, from -AA meals and 29.5% (23.3%, 38.2%) and 16.6% (12.8%, 21.7%) (P = 0.004), respectively, from +AA meals. Median percentage increases in iron absorption for -AA to +AA meals were 56% in the NW (P < 0.001) and 28% in OW/OB (P = 0.006). Serum ferritin [R(2) = 0.22; β = -0.17 (95% CI: -0.25, -0.09)], transferrin receptor [R(2) = 0.23; β = 2.79 (95% CI: 1.47, 4.11)], and hepcidin [R(2) = 0.13; β = -0.85 (95% CI: -1.41, -0.28)] were significant predictors of iron absorption.

CONCLUSIONS: In overweight and obese women, iron absorption is two-thirds that in normal-weight women, and the enhancing effect of ascorbic acid on iron absorption is one-half of that in normal-weight women. Recommending higher intakes of ascorbic acid (or other luminal enhancers of iron absorption) in obese individuals to improve iron status may have a limited effect. This trial was registered at clinicaltrials.gov as NCT01884506.