Technique for determination of human zinc absorption from measurement of radioactivity in a fecal sample or the body.

The intestinal absorption of an oral dose of zinc chloride was determined from the ratio of 65Zn and a nonabsorbed radioactive marker, 51Cr, present in a single stool specimen or the body 24-72 h later. Chromic chloride had no effect on [65Zn]zinc chloride absorption and 51Cr and 65Zn had similar intestinal transit times. In 17 healthy control subjects given 92 mumol ZnCl2 labeled with 0.5 microCi 65Zn, 52 +/- 14% (SD) of the dose was taken up from the lumen. Intestinal absorption of 65Zn at 24 h correlated closely with 65Zn body retention of zinc measured by whole-body counting 7 days later, r = 0.995. Neither zinc absorption nor zinc retention correlated with blood leukocyte zinc levels. An average of 55% of 65Zn was retained in the body from doses of 18-90 mumol ZnCl2 but a progressively smaller proportion of zinc was absorbed from doses of 180-900 mumol. The average absorption and body retention of 65Zn were significantly reduced in 7 patients with mucosal disease of the proximal intestine but they were not affected by resection of the lower jejunum, ileum, and colon. Thus the absorption of ZnCl2 from a 92-mumol dose predominantly takes place by a rate-limited mechanism in the duodenum and upper jejunum.