Nutritional zinc balance in extremely low-birth-weight infants

Zinc is important for metabolism, cell growth, immunity, and defense against oxygen radicals. Extremely low-birth-weight (< 1000 g) infants have higher nutritional needs, but information on zinc is scarce. The authors performed nutritional balances in 10 infants with birth weights of 500 to 999 g and who were fed with fortified human milk.

The authors collected infant feces, urine, and blood and human milk samples during 72 hours at 7 and 12 weeks of age. Zinc concentration was measured by inductively coupled plasma-mass spectrophotometry, atomic emission spectrophotometry, and instrumental neutron activation analysis.

Mean (SD) intake via human milk was 379 (+/- 373) microg x kg(-1) x d(-1) during both balances. Urinary excretion was high at 7 weeks of age, decreased to half at 12 week, and was negatively correlated (P < 0.01) with weight gain. Mean absorption was slightly positive at 7 weeks of age but zero or negative in most infants at 12 weeks of age. Retention was negative in all infants at both observation periods, except in one infant during the second balance. Clinical zinc deficiency developed in one infant at 12 weeks of age.

Zinc balances in extremely low-birth-weight infants are highly variable and usually negative. Controlled trials are needed to assess need for and benefits and risks of zinc supplementation.