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Human milk is the only source of nutrition for
exclusive breastfed infants during the first six months of life. Copper
(Cu) body stores are sufficient at birth to protect infant from
deficiency until 4-6 months, but zinc (Zn) body storages are not
extensive, and it should be taken in adequate quantities for
optimal growth and development [1]. Both Zn and Cu have critical roles
in infant growth [2,3]. There is some controversy about other clinical
determinants of breast milk Zn and Cu concentrations [4-8]. We aimed to
analyze Zn and Cu content in breast milk in Turkish mothers at the
second month of lactation, and to study the association of some maternal
and infant characteristics with breast milk Zn and Cu concentrations.
Methods
This study was conducted between August 2006 and
January 2007. Participitants were recruited from lactating mothers
attending Hacettepe University Ihsan Dogramaci Children Hospital in
Ankara, Turkey for routine well-baby visit at the second month (52-60
days postpartum). A total of 142 apparently well-nourished, consenting
mothers and their infants participated in the study. Mothers whose
nipples were cracked, and those having mastitis or using cream on nipple
were not taken into study. The study was approved by the Ethical
Committee of The Faculty of Medicine, Hacettepe University.
A questionnaire including maternal age, parity,
monthly family income, maternal smoking habits, and iron or
vitamin/mineral supplement intake during pregnancy and postpartum,
birthweight, gestational age, and delivery type was completed with all
mothers. Based on their smoking status, mothers were divided into two
groups as active tobacco use and/or passive exposure to smoke, and no
exposure to smoke. Postpartum maternal hemoglobin values, analysed at
the postpartum 1st
day, were noted from hospital record file. The infants weight, length,
and head circumference were recorded. The Z scores of weight-for-age,
length-for-age, head circumference for age, and body mass index for age
were calculated on the basis of recent WHO growth references.
Breastmilk samples were collected by manual
expression after about 2 hours from the last feeding session in the
morning. Concentrations of Cu and Zn were determined by Inductively
Coupled Plasma Mass Spectrometry (using an Agilent 7500a instru-ment).
The Limit of Quantitation (LOQ) for Zn and Cu were 0.8 µg/L. Data were
analyzed using the SPSS-Windows 10.0. Mann Whitney U test was applied to
compare the level of trace elements between sub-groups, as defined by
various maternal and infant characteristics. Statistical significance
was accepted at P<0.05.
Results
The mean age of mothers was 24.7 (ħ 5) years (range
17-41). Seventeen infants were preterm (gestational age <37 weeks) and
only nine infants had low birth weight (<2500g). The median (25-75
percentiles) concentrations of Zn and Cu were 625 (475-889)µg/L and 239
(200-296) µg/L, respectively. Milk Zn concentrations were not correlated
with milk Cu concentrations (r=0.09, P=0.310).
Maternal age, family income, parity, postpartum Hb
values, smoking habits at pregnancy and postpartum period, iron and
vitamin/mineral supplement intake at pregnancy and postpartum period
affected neither milk Zn nor Cu concentrations (Web Table I).
Further, birthweight, gestational age, and delivery type were not
associated with breastmilk Zn or Cu concentrations. 116 (86%) infants
were exclusively breastfed. The milk concentrations of Zn and Cu were
not different with regard to feeding types. There was no correlation
between breastfeeding practices (frequency of day and night time
suckling, and duration of breastfeeding) and milk Zn and Cu
concentrations.
Breastmilk zinc and copper concentrations of infants
having anthropometric measurements less than -2 z scores were not
different than those of z score
≥-2.
Breast milk Zn and Cu concentrations were also not correlated with the
anthropometric measurements.
Discussion
In the present study, the median concentration of Cu
in breast milk fell within the range of concentrations found in other
populations and only 13% were <180 µg/L, which is the WHO standard
concentration [1]. However, 56% of Zn concentrations were <700 µg/L
which is the WHO standard concentrations. There is a wide variation in
concentrations of breast milk Zn and Cu reported from different
countries [4-7]. The analysis method (ICP-MS, AAS, etc), sampling time
(foremilk-hindmilk or morning-afternoon-night), sampling method (pump,
manual suckling), between-breast (right, left) differences, the stage of
lactation, and inter-individual variability might be plausible reasons
for different results in previous studies [8-10].
The factors that affect breast milk Cu and Zn
concentrations are still controversial [4-10]. Previous studies
reported that maternal age, parity, smoking, delivery type, gestational
age, place of residence, and maternal body mass index might affect the
breast milk Cu and Zinc contents [5,6]. Our results were consistent with
previous studies with neither maternal factors nor infant factors being
associated with breast milk Cu and Zn concentrations [4,7]. However,
Mahdavi, et al. [11] reported that the weight for age z scores of
infants whose mothers milk zinc was more than 2 mg/L were significantly
higher than for others. Limitations of the present study include;
maternal diets were not evaluated, maternal serum Zn and Cu
concentrations were not analyzed, and the concentrations of Zn and Cu
were measured only one time during lactation.
In conclusion, it was found that our population had
lower breast milk zinc concentrations at two month of lactation whereas
breast milk copper concentrations were within references range. Breast
milk concentrations of Zn and Cu had no correlation with the examined
maternal and infant features.
Funding: This study was partially supported by
the Refik Saydam National Public Health Agency.
Competing interests: None stated.
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