Stable isotope studies of zinc absorption and retention in young and elderly men.
Level 3 - non-randomized controlled study
Non-randomized comparative cohort study comparing two age groups in a controlled metabolic unit
PubMed 3746461 · doi:10.1093/jn/116.7.1239
What was done
Six young men and six elderly men were confined to a metabolic unit for 12 weeks on a purified formula diet containing 15 mg of zinc per day. Zinc absorption was measured twice per subject using stable isotopes (67Zn and 70Zn). Serum, urinary, and fecal zinc and zinc balance were determined using atomic absorption spectrometry.
What was found
Zinc absorption averaged 17% in elderly men versus 31% in young men. Serum zinc was lower in elderly men and increased in both groups during the study. Net zinc balance did not differ between groups, and endogenous zinc losses were lower in elderly men compared to young men.
Why it matters
The study shows that while intestinal zinc absorption declines with age, homeostatic reductions in endogenous zinc excretion help preserve overall zinc balance under controlled intake.
Limits
The sample size is very small (n = 12 total, 6 per group) and included only men. The strictly controlled formula diet in a metabolic unit may not reflect habitual whole-food dietary patterns.
Cited by
- supports Intestinal absorption of zinc declines significantly with age, dropping by approximately half.