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ARS Home » Plains Area » Grand Forks, North Dakota » Grand Forks Human Nutrition Research Center » Dietary Prevention of Obesity-related Disease Research » Research » Publications at this Location » Publication #147580
Title: BIOAVAILABILITY OF ELEMENTAL IRON POWDERS TO RATS IS LESS THAN BAKERY-GRADE FERROUS SULFATE AND PREDICTED BY IRON SOLUBILITY AND PARTICLE SURFACE AREA

Author
item Swain, James
item Newman Jr, Samuel
item Hunt, Janet

Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2003
Publication Date: 11/1/2003
Citation: Swain, J.H., Newman Jr, S.M., Hunt, J.R. 2003. Bioavailability of elemental iron powders to rats is less than bakery-grade ferrous sulfate and predicted by iron solubility and particle surface area. Journal of Nutrition. 133:3546-3552.

Interpretive Summary: Iron is essential for normal growth, development, and performance of daily tasks. To reduce iron deficiency anemia and improve iron status, foods are fortified with iron. Commonly, elemental iron powders from the metallurgy industry are used for fortification because they are economical and do not adversely affect the fortified food (i.e., cause color and flavor changes). Foods typically fortified with elemental iron powders include ready-to-eat breakfast cereals and cereal grains. To evaluate six commercial elemental iron powders used widely as food fortificants today, we tested how effective they were for treating iron deficiency anemia in rats. The results show that these commercial iron powders were only 21 to 64 as effective as ferrous sulfate which is known to be well absorbed. The effectiveness of the iron powders was related to their solubility in dilute acid and even more so to the surface area of the particles. These findings, together with data in humans and information on commercial pricing of elemental iron powders, can assist in the development of qualitative and quantitative recommendations for fortification of foods with elemental iron powders.

Technical Abstract: Background: Foods are fortified with elemental forms of iron to reduce iron deficiency. However, the nutritional efficacy of current, commercially-produced elemental iron powders has not been verified. Objective: To determine the bioavailability of six commercial elemental iron powders and how physicochemistry influences bioavailability. Design: Relative biological value (RBV) of the iron powders was determined by a hemoglobin repletion/slope ratio method in weanling, male Sprague-Dawley rats. After dietary iron depletion, rats consumed repletion period diets fortified with graded quantities of iron powder, bakery-grade ferrous sulfate, or no added iron. Iron powders were assessed physicochemically by measuring iron solubility in 0.02 M hydrochloric acid and surface area by nitrogen gas adsorption; surface microstructure was investigated by scanning electron microscopy. Results: Relative to FeSO4, 100%a, iron bioavailability from the powders was less: Carbonyl (FerronylJ, U.S.), 64%b; Electrolytic (A-131, U.S.), 54%c; Electrolytic (Electrolytic Iron, India), 46%cd; H-reduced (AC-325, U.S.), 42%d; Reduced (ATOMET 95SP, Canada), 24%e; and CO-reduced (RSI-325, Sweden), 21%e (values with different letters significantly differ (p<0.05)). Solubility ranged from 10 to 60% at 15 min and 51 to 97% at 150 min, but the rank/order was inconsistent at different times. Surface area of the powders ranged from 90 to 370 m2/kg. Solubility accounted for 36 to 65%, whereas surface area accounted for 80% of the variation in RBV. Conclusions: Bioavailability of iron powders is less than bakery-grade ferrous sulfate and varies up to 3-fold among various commercial forms. Surface area more reliably predicts the bioavailability of elemental iron powders than solubility in dilute acid.