Submitted to: Journal of the American College of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2008
Publication Date: 10/15/2009
Citation: Beisiegel, J.M., Klevay, L.M., Johnson, L.K., Hunt, J.R. 2009. Zinc Absorption Adapts to Zinc Supplementation in Postmenopausal Women. Journal of the American College of Nutrition. 28(2):177-183.
Interpretive Summary: U.S. adults commonly use daily zinc supplements. In the short-term, the more zinc is consumed, the more is absorbed. This study was conducted to learn if people adapt after several weeks to decrease the amount of zinc absorbed. Sixteen healthy postmenopausal women consumed a controlled, low-zinc diet (3-6 mg/d) supplemented daily with moderate to high doses of zinc (9, 27, or 42 mg Zn/d) for 22 wks. Their total zinc absorption was measured at 0, 8, and 16 wks. The women whose diets were supplemented with 9 mg/d absorbed about 5 mg per day throughout the study. In contrast, the women supplemented with the 27 or 42 mg Zn/d absorbed about twice this much initially, but their absorption of zinc continually decreased, so that absorption differences between the women were statistically insignificant by 8 weeks and were negligible by 16 weeks, with all women absorbing approximately 5 mg/d. Plasma zinc increased with doses of 27 mg/d and 42 mg/d but not with 9 mg/d. Zinc supplementation did not affect copper status or blood lipid measurements. In conclusion, healthy postmenopausal women adapt to finely control zinc absorption so that similar amounts of zinc are absorbed from moderate and high doses.
Technical Abstract: Objective: To determine if human Zn absorption adapts to chronic high Zn intakes. Methods: Zn absorption was measured at 0, 8, and 16 wk in healthy postmenopausal women who consumed controlled diets with ~5 mg Zn from food, supplemented to 14 (n = 6), 32 (n = 3), or 47 (n = 3) mg Zn/d for 22 wk. Zn absorption for 1 day was determined by 65Zn-labeling of meals and whole body scintillation counting. Results: At wk 0, less Zn was absorbed from diets with 14, compared with 32 or 47 mg/d (4.6, 8.7, and 10.3 mg/d, respectively; pooled SE = 0.9; p<0.05). These differences were not apparent at wk 8 (5.4, 5.8, 6.4; NS) and became negligible by wk 16 (5.0, 5.0, 5.1; NS). Plasma Zn concentrations were unaffected. The results are consistent with a saturation response model of Zn absorption. Conclusion: Within several weeks, postmenopausal women biologically adapted to absorb a relatively uniform amount of 5 mg Zn/d when controlled, Zn-supplemented diets supplied consistent Zn intakes between 14 and 47 mg/d.