Iron supplement use and iron status among US adults: results from the third National Health and Nutrition Examination Survey

Background: Patients with hemochromatosis are instructed to avoid taking supplemental iron. Whether supplemental iron intakes lead to higher iron status among healthy persons remains less clear. Objective: The objective was to ascertain whether supplemental iron intakes are associated with increases in iron transport (transferrin saturation) and stores (serum ferritin) among US adults aged >= 19 y. Design: We analyzed data for 5948 adults from whom a fasting serum sample was collected during the third National Health and Nutrition Examination Survey. We used multivariable linear regression and analysis of variance to assess the association of supplemental iron intake with iron transport and stores among men (aged 19-30 y or > 30 y) and women (nonpregnant premenopausal or postmenopausal); multiple comparison tests were also performed. Results: Healthy adults who took supplements containing average daily amounts of iron at :5 3 times the recommended dietary allowance (RDA) did not have significantly higher iron transport or stores than did those who did not take supplements. In younger men, the intake of > 32 mg Fe/d (> 4x RDA) was associated with mean transport iron concentrations that were significantly higher than those in persons who took 0 to <= 24 mg Fe/d. In older men, the intake of > 32 mg Fe/d (> 4x RDA) was associated with mean iron stores that were significantly higher than those in persons who took 0 to <= 24 mg Fe/d; a similar result was observed in postmenopausal women, but it was of borderline statistical significance. Conclusion: Supplement users should be made aware of the amount of iron necessary to satisfy dietary requirements and informed of the possible influence that excess iron intake can have on body iron stores and health.