Determination of zinc and copper absorption at three dietary Zn-Cu ratios by using stable isotope methods in young adult and elderly subjects.
Level 3 - non-randomized controlled study
Non-randomized controlled crossover metabolic study
PubMed 2596436 · doi:10.1093/ajcn/50.6.1457
What was done
Nine young men and six elderly men and women ingested low-zinc, low-copper, and adequate diets for 2-wk periods, with zinc-to-copper ratios averaging 2:1, 15:1, and 5:1. On day 8 of each period, subjects ingested stable isotope doses of 70Zn and 65Cu to measure net absorption.
What was found
On the adequate diet, zinc absorption was 39 ± 3% in young subjects and 21 ± 1% in elderly subjects (p < 0.05). During the low-zinc period, zinc absorption rose to 64 ± 5% in young and 43 ± 7% in elderly subjects (both p < 0.05 vs adequate). Copper absorption on the adequate diet was 60 ± 4% in young and 53 ± 2% in elderly subjects. During the low-copper period, copper absorption increased to 67 ± 4% in elderly subjects (p < 0.05) and was higher in 6 of 7 young subjects (p > 0.05). Changes in zinc-to-copper ratios had less effect on absorption than dietary restriction.
Why it matters
It demonstrates that baseline zinc absorption decreases with age, but older adults retain the homeostatic capacity to upregulate zinc and copper absorption when dietary intake is restricted.
Limits
The sample size is very small (n = 15 total), the young group included only men while the elderly group included both sexes, and the abstract does not state whether diet sequence was randomized.
Cited by
- supports Intestinal absorption of zinc declines significantly with age, dropping by approximately half.