Determination of zinc and copper absorption at three dietary Zn-Cu ratios by using stable isotope methods in young adult and elderly subjects.

Nine young men and six elderly men and women ingested low-zinc, low-copper, and adequate diets for 2-wk periods. The Zn-Cu ratios averaged 2:1, 15:1, and 5:1. On day 8 of each period, subjects ingested doses of 70Zn and 65Cu so that net absorption could be determined. Zn absorption on the adequate diet was 39 +/- 3% (means +/- SEM) in young subjects and 21 +/- 1% (p less than 0.05) in the elderly subjects. During the low-Zn period, Zn absorption was higher as compared with that on the adequate diet in both young (64 +/- 5%, p less than 0.05) and elderly subjects (43 +/- 7%, p less than 0.05). Cu absorption on the adequate diet was 60 +/- 4% and 53 +/- 2% in young and elderly subjects, respectively. During the low-Cu period, Cu absorption was higher as compared with that on the adequate diet in the elderly subjects (67 +/- 4%, p less than 0.05). Cu absorption was higher in six of seven young subjects on the restricted Cu diet (p greater than 0.05). The effect upon absorption of the change in the Zn-Cu ratio was less than the effect of dietary restriction.