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ARS Home » Plains Area » Grand Forks, North Dakota » Grand Forks Human Nutrition Research Center » Healthy Body Weight Research » Research » Publications at this Location » Publication #149022
Title: DIETARY IRON AND CALCIUM INTERACT TO AFFECT IRON STATUS AND BONE HEALTH IN A RESPONSE SURFACE STUDY OF GROWING FEMALE RATS

Author
item Roughead, Zamzam
item JOHNSON, L. - UNIV OF NORTH DAKOTA
item WAGNER, J. - UNIV OF NORTH DAKOTA

Submitted to: Journal of Bone and Mineral Research
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2003
Publication Date: 9/19/2003
Citation: Roughead, Z.K., Johnson, L.K., Wagner, J.L. 2003. Dietary iron and calcium interact to affect iron status and bone health in a response surface study of growing female rats [abstract]. Journal of Bone and Mineral Research. 16:S155.

Interpretive Summary:

Technical Abstract: The concerns about inadequate intakes of calcium (Ca) and iron (Fe) have led to extensive fortification of both minerals in the US food supply. The objective of this study was to test the interaction of Ca and Fe over a wide range of intakes using a two-factor central composite response surface design. Weanling female Sprague-Dawley rats (n= 44) were randomly assigned to 9 groups fed AIN-93G basal diets with varying amounts of Fe (3, 5, 17, 60, or 100 ug/g diet), and Ca (1000, 1330, 2646, 5264, or 7000 ug/g diet) for 7 weeks. Semi-partial correlation coefficients were obtained by stepwise regression analysis and reported at a significant level of p<0.02. Iron status (hemoglobin, hematocrit, red cell distribution, liver nonheme Fe) was primarily determined by dietary Fe (R2p=0.92, 0.93, 0.81, and 0.78, respectively). However, increased Ca intake had an antagonistic effect on Fe status such that, based on the regression model, the predicted maximum hemoglobin of 16.8 g/dL occurred when Fe intake was moderate (43.5 ug/g diet) and Ca intake was minimal (1000 ug/g diet). Although Ca intake was the primary determinant of femur density, accounting for 79% of its variability, Fe intake also affected femur density (R2p = 0.10). Femur density was maximal at moderate intakes of Fe and Ca (38 and 4963 ug/g diet, respectively) and decreased slightly with higher intakes of both minerals. Variability in femur breaking strength (N/mm2) was determined only by Ca intake (R2p = 0.70), was maximal with moderate Ca intake of 4120 ug/g diet, and decreased with further increases in Ca intake. While the main constituents of bone matrix (Ca and collagen) were only affected by dietary Ca (R2p = 0.42, 0.28, respectively), certain noncollagenous components in bone (osteocalcin, hexosamines) responded to changes in both Ca and Fe intakes. Serum concentrations of insulin-like growth factor-1 (IGF-1) did not respond to either dietary Ca or Fe, but bone IGF-1 concentration was weakly associated with dietary Ca (R2 = 0.26). In summary, in growing female rats, high Ca intake reduced Fe status. While adequate intakes of both Ca and Fe were essential for maximal bone density, excessive intakes of these minerals reduced bone density and strength. In conclusion, the effects of high Ca intake on Fe status were more pronounced than the effects of Fe nutriture on bone health. These findings indicate that Ca intakes above the adequate amount do not offer additional benefits and may even be detrimental to bone. Additionally, indiscriminate fortification of foods with Ca may compromise the Fe status of vulnerable segments of the population.