The concentration of essential trace elements in breast-milk is an
important topic in infant nutrition. The interesting paper by Örun,
et al.  needs to be put in context in the light of previous
research on the topic. Comprehensive reviews of breastmilk zinc [2,3]
and copper  concentrations have addressed the maternal
(constitutional and environmental) factors modulating the secretion of
these essential nutrients. I was surprised that the brief discussion by
Örun, et al.  overlooked these sources. Also, compared to
international data, they showed a surprisingly low mean milk-zinc
I take the opportunity to remind readers that in the
case of zinc, the stage of lactation is the only variable associated
with important changes in milk concentrations. In the first days
postpartum, the zinc concentrations in breast-milk fall steeply, and
after the first weeks, gradually decrease throughout the following 6
weeks; reaching relatively stable levels by the third month. In spite of
increasing volumes of milk consumed by nursing infants, the total zinc
intake falls as a function of the rate of decrease in the milk metal
concentration. For postpartum days 1, 7, 15, 30, 60, 90, 120, and 180,
the reported median zinc concentrations (mg/L) are 8.12, 4.56, 3.36,
2.65, 1.66, 1.35, 1.2, 0.98 and 0.93; respectively . Experiments with
maternal zinc supplementation aimed at enriching breast-milk have not
been effective. However, maternal zinc therapy has been reported to
correct abnormalities of zinc metabolism during gestation and lactation
The variability of breast-milk zinc concentrations is
wide; it does not depend on maternal zinc intake but it can vary within
and between mothers as a function of parity, stage of lactation, and
type (fore or hind milk) of feeding . Therefore, to test a hypothesis
that a significant association exists between this variable and
anthropometry (changing in the opposite direction) requires a more
appropriate study design. However, it is possible that repeated
measurements of both milk zinc and anthropometry in exclusively
breastfed infants, as in follow-up studies, has been useful in
generating the hypothesis that the decrease in zinc concentrations can
be associated with weight and linear growth .
1. Örun E, Yalçin SS, Aykut O, Orhan G, Morgil GK.
Zinc and copper concentrations in breastmilk at the second month of
lactation. Indian Pediatr. 2012;49:133-5.
2. Dórea JG. Is zinc a first limiting nutrient in
human milk? Nutr Res. 1993;13:659-66.
3. Dórea JG. Zinc in human milk. Nutr Res.
4. Dórea JG. Iron and copper in human milk.
5. Dórea JG. Zinc deficiency in nursing infants. J Am Coll Nutr.