Changes in regulation of human zinc metabolism with age

To assess changes in zinc metabolism with age, kinetic studies were performed in healthy adults (26 men, 21 women) aged 20-84 yr after a single oral or intravenous bolus of 65Zn. Studies covered two consecutive 9-mo periods while subjects were on a basal dietary intake of approximately 10 mg Zn/day and while taking an additional 100 mg Zn/day orally. Zinc metabolism was analyzed by compartmental analysis using data from plasma, red blood cells, urine, feces, liver, thigh, and whole body [M. E. Wastney, R. L. Aamodt, W. F. Rumble, and R. I. Henkin. Am. J. Physiol. 251 (Regulatory Integrative Comp. Physiol. 20): R398-R408, 1986]. Changes in observed and model calculated values of zinc metabolism were assessed on age by regression. During basal state, zinc release from red blood cells decreased with age. During zinc loading, response (defined as change from basal state) of plasma zinc concentration, urinary zinc excretion, and liver zinc increased with age, while response of fraction of zinc taken up by red blood cells decreased with age. In men, response of amount of zinc absorbed increased with age and in women response of fraction of endogenous zinc excreted decreased with age. Four responses that changed with age (urinary excretion, red blood cell exchange, absorption, and endogenous excretion) occurred at previously defined sites of regulation of zinc metabolism. Results show that regulation of zinc metabolism changes with age.