Abnormal zinc content in human milk. Risk for development of nutritional zinc deficiency in infants
S. A. Atkinson, D. Whelan, R. K. Whyte and B. Lonnerdal
Department of Pediatrics, McMaster University, Hamilton, Canada.
An abnormally low concentration of zinc in mother's milk has been
associated with clinical nutritional zinc deficiency in premature and term
newborns. Defective mammary gland secretion of zinc was suggested as the
causative factor. We investigated whether low milk zinc concentration might
be reflected in an abnormality of the distribution of zinc between casein,
whey, and fat components of the milk, in a reduction in the levels of milk
citrate, a zinc-binding ligand, or in abnormal levels of copper and iron.
Milk from mothers of four low-birth-weight infants was identified as being
deficient in zinc content for the lactational stage. One infant had
clinical signs of nutritional zinc deficiency. For two of the three infants
with subclinical deficiencies in whom balance study data were available,
the apparent zinc balance was negative (-5.7 and -6.0 mumol/kg per day).
These milks were examined for content and distribution of zinc, copper, and
iron, and citrate concentration. Although total zinc concentration (4.5 to
17.2 mumol/L) was below the 95% prediction interval (15.2 to 59.7 mumol/L)
for the lactational stage, the distribution of zinc was normal between milk
components. Levels of citrate (1.46 to 5.13 mmol/L) were also within normal
limits, as were levels of copper (0.27 to 0.85 mumol/L and iron (0.41 to
1.13 mumol/L). We concluded that there was no indirect evidence of a
secretory abnormality in milk zinc deficiency, but speculated that there
might instead be an abnormality of zinc uptake by the mammary gland from
the plasma.
