ARS | Publication request: Women's zinc absorption is unaffected by dietary calcium, with or without high-phytate foods

Submitted to: Cell Biology and Toxicology
Publication Type: Abstract
Publication Acceptance Date: August 15, 2007
Publication Date: September 1, 2008
Publisher's URL: http://www.springerlink.com
Reprint URL: http://www.springerlink.com
Citation: Hunt, J.R., Beiseigel, J. 2008. Women's zinc absorption is unaffected by dietary calcium, with or without high-phytate foods [abstract]. Cell Biology and Toxicology. 24(Suppl 1):S21

Technical Abstract: While some have hypothesized that calcium increases the inhibitory effect of phytic acid on zinc absorption by forming insoluble Ca-Zn-phytate complexes, others have suggested that calcium may competitively bind phytic acid, reducing the phytic acid inhibition of zinc absorption. We tested the influence of approximately 700 (LCa) or 1900 (HCa) mg/d dietary calcium with 440 (LP) or 1800 (HP) mg/d phytic acid on zinc absorption in a 2x2 factorial design. Minerals were measured by ICAP and phytic acid by the AOAC extraction and ion-exchange method. The weighed diets, consisting of ordinary foods, contained ~11.5 mg Zn/d, with a phytate:Zn molar ratio of ~4 for LP and 15 for HP. Zinc absorption from each of the four 1-day menus was determined with 10 healthy women by extrinsically labeling the foods with 65Zn and measuring retention by whole body scintillation counting. For each absorption measurement, individual differences in endogenous Zn excretion were corrected for by extrapolating back to baseline along the linear portion of a 4-week semi-logarithmic retention curve. Data were analyzed by ANOVA with Tukey¿s pair-wise contrasts. Zinc absorption from the LCaLP, LCaHP, HCaLP, and HCaHP diets, was 33, 27, 39, and 26% (pooled SD= 7.6), or 3.8, 3.0, 4.5, and 3.2 mg/d (pooled SD= 0.28), respectively. Phytic acid significantly decreased zinc absorption (p<0.001), but calcium did not, nor did calcium significantly interact with phytic acid. We conclude that calcium in the range normally consumed, even with calcium-fortified diets, does not interfere with Zn absorption.