Zinc tolerance tests in chronic uremia

The intestinal absorption of zinc was investigated in 12 control subjects and in 20 patients on maintenance hemodialysis by means of a zinc tolerance test during fasting. Ten patients (Group I) were on long-term vitamin D therapy and 10 (Group II) were not receiving vitamin D. After baseline plasma zinc measurements, a single dose of 50 mg zinc was ingested and plasma zinc levels were measured at hourly intervals for 4 hours thereafter. Peak plasma zinc levels were significantly lower in Group II patients than in controls or patients in Group I suggesting impaired absorption. No significant difference was found between controls and Group I patients. Two patients had normal zinc tolerance tests while on vitamin D therapy, but abnormal tests while off vitamin D. We conclude that the intestinal absorption of zinc may be impaired in chronic uremia, probably secondary to abnormal metabolism of vitamin D.