Zinc Homeostasis in Breast-Fed Infants

Abstract

The needs for dietary zinc are adequately met by most fully breast-fed infants despite relatively low zinc intakes in relation to estimated requirements. The objective of this study was to use stable isotope techniques to evaluate how zinc retention is achieved in normal fully breast-fed infants. Nine male infants, aged 2-5 mo, were fed expressed human milk labeled with 70Zn over a 24-h period. Complete fecal collections were obtained for 8 d. On d 4-7, a metabolic period was initiated which included test weighing and milk sampling, to measure zinc intake, and daily urine collections. Isotopic enrichment of fecal and urine samples was determined by fast atom bombardment mass spectrometry. Results included a mean (+/- SD) dietary zinc intake of 17.8 +/- 6.6 mumol/d; fractional absorption of 0.54 +/- 0.075; and total absorbed zinc of 9.5 +/- 3.5 mumol/d. Mean endogenous fecal zinc, determined on seven infants by isotope dilution, was 4.7 +/- 2.3 mumol/d, which resulted in a mean net absorption of 4.8 +/- 3.4 mumol/d. The results of the study indicated that, for fully breast-fed infants, it is the combination of a relatively high fractional absorption and efficient conservation of intestinal endogenous zinc that results in zinc retention adequate to meet the demands of growth in the face of modest intake.

Abnormalities in Zinc Homeostasis in Young Infants with Cystic Fibrosis

“…The mean fractional absorption of dietary zinc in these infants was substantially lower than figures reported for normal breast-fed and formula-fed infants (10,19,20) of similar age. For normal exclusively breast-fed infants ranging in age from 2-4 mo, fractional absorption averaged 0.54 Ϯ 0.08 (10).…”

“…Milk, stool, and urine analyses for total zinc and isotopic enrichment were performed as previously described (9,10). Fecal samples before and after the metabolic period were pooled into 12-h homogenates.…”

Zinc Homeostasis in Premature Infants Does Not Differ Between Those Fed Preterm Formula or Fortified Human Milk

“…Endogenous fecal zinc excretion measured in this study by isotope dilution was considerably lower than in several previous reports in premature infants (5,7), but was nearly twice that of term formula-fed infants (17) and approximately 4-fold greater than that of term exclusively breast-fed infants (11). Methodological differences may again account for differences between studies in preterm infants, since some have relied on a difference of net absorption, derived from mass balance data, and absorbed zinc determined with stable isotopes (5).…”

“…The addition of human milk fortifier to the expressed human milk provided intakes well within the recommended range and to levels that were ‫%58ف‬ of those fed the preterm infant formula. For comparison, the zinc intakes of these preterm infants, on a body weight basis, were nearly double that of term formula fed infants (17), and 5-to 6-fold that of term breast-fed infants (11).…”

Íon zinco: presença no sistema auditivo

“…(Prasad, 1995; Valee e .alchuk, 1993). A quantidade de zinco aumenta de 1 a 3 vezes, devido à soma com o zinco contido no sucos digestivos; a absorção parece ser por difusão passiva, porém mediado por carreadores enzimáticos (Krebs et al, 1996). Ao nível da superfície serosa baso-lateral das células intestinais, o zinco é liberado para a luz dos capilares mesentéricos, sendo levado para o sistema porta e depois para o fígado.…”