Few data have evaluated Zn balance in young children after the first year of life. The objective of the present study was to study the relationships among Zn intake, absorption, endogenous faecal excretion, and retention in a group of healthy children. Thirty children, aged 15–48 months, were studied on a diet representative of their usual daily mineral intake. Zn absorption was assessed using a dual-tracer stable-isotope technique. Endogenous Zn faecal excretion and Cu absorption were determined in a subset of children. We found that Zn intake from the in-patient weighed dietary record (5·0 (sd 2·1) mg/d) was significantly greater than the current estimated average requirement (EAR; 2·5 mg/d; P < 0·0001). Neither fractional Zn absorption, urinary Zn excretion, nor endogenous faecal Zn excretion was significantly related to Zn intake (r2 < 0·1; P>0·4, for all). Absolute Zn absorption was significantly related to Zn intake (r2 0·696; P < 0·0001), as was Zn retention (r2 0·506; P < 0·0001). Cu absorption was relatively high (75·1 (sd 10·8) %) despite the high Zn intake. The EAR for Zn based on this dataset would appear to be between 4·2 and 4·7 mg/d to allow for a net average retention of 120 μg/d consistent with growth needs. We concluded that at relatively high Zn intakes there was little evidence of down regulation of absorption or up regulation of urinary or endogenous faecal Zn excretion across the intake range studied. Zn retention was positively correlated with intake. A Zn intake between 4·2 and 4·7 mg/d should meet the requirement for normal growth for this age group.

The study of Cu metabolism is hampered by a lack of sensitive and specific biomarkers of status and suitable isotopic labels, but limited information suggests that Cu homeostasis is maintained through changes in absorption and endogenous loss. The aim of the present study was to employ stable-isotope techniques to measure Cu absorption and endogenous losses in adult men adapted to low, moderate and high Cu-supplemented diets. Twelve healthy men, aged 20–59 years, were given diets containing 0·7, 1·6 and 6·0 mg Cu/d for 8 weeks, with at least 4 weeks intervening washout periods. After 6 weeks adaptation, apparent and true absorption of Cu were determined by measuring luminal loss and endogenous excretion of Cu following oral administration of 3 mg highly enriched 65Cu stable-isotope label. Apparent and true absorption (41 and 48% respectively) on the low-Cu diet were not significantly different from the high-Cu diet (45 and 48% respectively). Endogenous losses were significantly reduced on the low- (0·45mg/d; P<0·001) and medium- (0·81 mg/d; P=0·001) compared with the high-Cu diet (2·46mg/d). No biochemical changes resulting from the dietary intervention were observed. Cu homeostasis was maintained over a wide range of intake and more rapidly at the lower intake, mainly through changes in endogenous excretion.