http://informahealthcare.com/ijf ISSN: 0963-7486 (print), 1465-3478 (electronic) Int J Food Sci Nutr, 2014; 65(5): 547–551 ! 2014 Informa UK Ltd. DOI: 10.3109/09637486.2014.893281
FOOD COMPOSITION AND ANALYSIS
Trace element compositional changes in human milk during the first four months of lactation Carla Matos1, Carla Moutinho1,2, Cristina Almeida1, Anto´nio Guerra3, and Victor Balca˜o2,4 Int J Food Sci Nutr Downloaded from informahealthcare.com by Bascom Palmer Eye Institute on 12/26/14 For personal use only.
1
Faculdade de Cieˆncias da Sau´de, Universidade Fernando Pessoa, Porto, Portugal, 2IBB – Instituto para a Biotecnologia e a Bioengenharia, Centro de Engenharia Biolo´gica, Universidade do Minho, Braga, Portugal, 3Departamento de Pediatria Faculdade de Medicina do Porto/HPI - Centro Hospitalar de Sa˜o Joa˜o, Alameda Prof. Hernaˆni Monteiro, Porto, Portugal, and 4Universidade de Sorocaba, Cidade Universita´ria, Sorocaba – SP, Brazil Abstract
Keywords
The aims of this paper were to evaluate changes in specific oligoelements in human milk during the first four months of lactation and to correlate such changes with total antioxidant status (TAS) and other parameters, such as the mother’s age, primipara versus multipara, and supplement intake. Milk samples were collected from 31 lactating women following 1, 4, 8, 12 and 16 weeks after birth. Trace levels of 13 elements were measured by inductively coupled plasma-mass spectrometry (ICP-MS). The results obtained for the oligoelements exhibited a decrease in concentration from 7 days to 4 months of breast-feeding, with exceptions. Correlations were found between TAS and Co, V, Rb and Tl. Between primipara and multipara, differences were found for Ni and Rb. Regarding the mother’s age, correlation was found for Rb and Ba (increased for mothers older than 30 years). Increased amounts of Rb, Mo and Tl at any lactation period appeared in women who took supplements.
Human milk, total antioxidant status, toxic metals, trace elements
Introduction Human milk is regarded as the ideal nutrient source for the growth and development of the infant, with unique composition characteristics, distinct from either bovine milk or infant formulae (Aycicek et al., 2006; Quiles et al., 2006). It has been reported that human milk can repress oxidative stress and oxidative DNA damage in newborn infants more effectively than infant formula which indicates that human milk contains a unique defence mechanism, which is not presented either in commercial or bovine milks (Lesniewicz et al., 2010; VanderJagt et al., 2001). Breastfed infants have reduced incidences of certain diseases, mainly neonatal sepsis, gastroenteritis, urinary and respiratory infections, and lower risk of obesity, when compared to formula-fed infants (Qian et al., 2010). It is well known that the composition of human milk is influenced by many factors and varies both within and between individuals. For example, trace element and macronutrient levels may differ with respect to the timing of delivery, maternal diet and age, parity, residing area and period of lactation (Li et al., 2005). Notwithstanding the fact that mother’s milk is seen as a perfect nutrient source for the newborn, human milk can also be a pathway of maternal excretion of toxic elements. In fact, many chemicals can be transferred from both the body reserves and the blood into the breast milk of a lactating mother. In this respect, the levels of toxic metals in milk are of significance Correspondence: Prof. Carla Matos, Grupo de Investigac¸a˜o em Bioengenharia e Quı´mica Biofarmaceˆutica, Faculdade de Cieˆncias da Sau´de, Universidade Fernando Pessoa, Prac¸a 9 de Abril n 349, P-249004 Porto, Portugal. Tel: +351-225074630. Fax: +351-225074637. E-mail: [email protected]
History Received 28 July 2013 Revised 23 January 2014 Accepted 7 February 2014 Published online 10 March 2014
(Koizumi et al., 2008; Wappelhorst et al., 2002). Cadmium, lead, arsenic and aluminium are of considerable interest due to their toxicity and widespread use (Ahamed et al., 2007; Al-Saleh et al., 2003; Garcı´a-Esquinas et al., 2011; Honda et al., 2003; Rahimi et al., 2009). The aim of this study was to determine rubidium (Rb), cobalt (Co), nickel (Ni), vanadium (V), chromium (Cr), molybdenum (Mo), barium (Ba), thallium (Tl), beryllium (Be), aluminium (Al), arsenic (As), lead (Pb) and cadmium (Cd) concentrations in the breast milk of healthy lactating women, during the first four months of lactation, who were living in Porto, Portugal, and to investigate the effect of mother’s age, parity and maternal supplementation of antioxidant vitamins or minerals on the concentration of those (essential, non-essential and toxic) elements. Since some trace elements, which can act as redox catalysts (namely, Ni, Co, Mo), may also be able to act as antioxidants, correlation between the metal concentration changes and the contents in total antioxidant status (TAS) was also evaluated.
Patients and methods Subjects This study was conducted with lactating women (n ¼ 102) who attended the Service of Obstetrics of Hospital de Sa˜o Joa˜o (HSJ) in Porto, Portugal. Healthy women who gave birth to healthy full-term infants were eligible for entry in this study. However, only women who clearly expressed the intention of exclusively breastfeeding their babies during their first 4 months of life were approached. Women were consecutively invited to participate in the study according to the criteria described hereafter. Regarding the
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Int J Food Sci Nutr, 2014; 65(5): 547–551
Table 1. Descriptive data relating to lactating mothers (n ¼ 31) and anthropometric values of suckling babies (n ¼ 31) at 0 days after birth.
Gestational age of baby (weeks) Maternal age (years) Parity Baby weight (g) Baby length (cm) Baby HC (cm)
Mean ± SD
Amplitude (min.–max.)
39.1 ± 1.3 30.9 ± 3.9 0.6 ± 0.7 3318 ± 467 49.6 ± 1.7 34.1 ± 1.3
37.0–42.0 21–39 0–2 2525–4090 45.0–53.0 31.0–36.0
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HC ¼ Head Circumference; SD ¼ Standard Deviation.
mothers, the inclusion criteria were (i) to have had a watched over gestation, (ii) to have decided to breast-feed the baby, and (iii) to live in Porto, and the criteria for exclusion were (i) to have a pathology preventing breast-feeding (tumour, HIV carrier, hepatitis B or C carrier), (ii) to be under pharmacological therapy preventing breast-feeding, and (iii) not willing to, or prevented from, breast-feeding. Concerning the babies, the criteria for inclusion were: (i) to have an adequate weight to the gestational age, (ii) to be a term newborn (gestation equal or higher than 37 weeks), and (iii) to be exclusively breast-fed during all the study or at least during the first four months of age, while the criteria for exclusion were: (i) being a premature or preterm newborn, (ii) having pathologies or intercurrences preventing breast-feeding or that interfered with normal growth (neurological and metabolic diseases, polymalformative syndromes, congenital cardiopathies, or others preventing breast-feeding), and (iii) being term newborns but possessing inadequate weight (either low or high) for the gestational age. The study was approved by the Hospital Ethical Committee and all the participating women gave their written informed consent. One hundred and two (102) lactating women gave their consent to participate in the study after explanation of the procedures, but only thirty-one (31) completed the study. The reasons for this were several and diverse in nature: nipple discomfort, lack of milk after only a few days or weeks, reduced availability for breast-feeding. For those 31 women, all infants were exclusively breast-fed on demand for 4 months. The ages of the women ranged between 21 and 39 years old, as shown in Table 1. Milk samples Breast milk samples were collected from each breast (by either breast pump or hand expression) before and after each feed, over a 24-h period. Samples were collected several times during one day (after 1, 4, 8, 12 and 16 weeks after birth) to sterile, and tracemetals free, plastic containers, kept refrigerated at 4 C and pooled together to produce a milk sample for that day, for the analysis. Samples were homogenized and stored in a household freezer for a maximum of 24 h, until transport on ice to the research laboratory, where they were stored at 80 C until analysis was in order. Determination of trace metals Trace metals were determined by the inductively coupled plasmamass spectrometry (ICP-MS). Ultrapure water (R418 M m1) obtained through a Milli-QTM system (Millipore; Billerica, MA) was used in the preparation of all solutions. All reagents used were obtained from Fluka (Buchs SE, Switzerland) and were of analytical grade or better, except for nitric acid, which was of SuprapurÕ grade (Merck, Darmstadt, Germany). Adequately acid-washed plastic materials were used at all times to avoid contamination during sample preparation. Milk analysis was performed by using a VG Elemental (Winsford, UK), PlasmaQuad 3 ICP-MS, equipped with a
Table 2. Main instrumental and operating conditions for ICP-MS analytical equipment. Instrument parameter Detector Detection mode Acquisition mode Rf power (W) Nebuliser gas flow (L/min) Auxiliary gas flow rate (L/min) Cool gas flow (L/min) Acquisition mode Sweeps Dwell time (ms) Channels per mass Channel spacing Replicates
Condition Sequential Pulse counting Continuous 1350 0.78 0.60 13.0 Peak jumping 200 10 1 0.02 2
MeinhardÕ type A pneumatic concentric nebuliser, a quartz water cooled impact-bead spray chamber, a standard quartz tube torch and nickel sample and skimmer cones. Both the spray chamber and sampling interface were cooled down to 10 C by circulating water. Argon of 99.9999% purity (Alphagaz 2TM, supplied by Air Liquide, Maia, Portugal) was used as plasma source. For ICP-MS waste draining, a Gilson Minipuls 3 (VilliersLe Bel, France) peristaltic pump was used. The ICP-MS operation and data acquisition was accomplished by using PlasmaLabÕ software (MUSA, Waltham, MA). The main operating conditions for the ICP-MS determinations are indicated in Table 2. Samples were analysed after microwave oven (Milestone, model MLS 1200 mega, Gemini BV, Haaksbergen, The Netherlands) digestion in teflon vessels (2 g of milk added with 1 mL of 65% HNO3 and 1 mL of 30% H2O2). ICP-MS calibration solutions were prepared by dilution of commercial solutions (AccuTraceTM Reference Standard, ICPMS-200.8-CAL1R-1; Atomic Spectroscopy Standard Solution V 70008, Fluka, Buchs SE, Switzerland, for Ba; and Rubidium atomic absorption standard solution 1000 mg/mL, Sigma-Aldrich Co., St. Louis, MO, for Rb). Internal standards (Sc, Y, In, Tb and Bi) were added to the diluting solutions via dilution of a commercial aqueous solution (AccuTraceÔ Reference Standard, ICP-MS-200.8-IS-1), in order to attain a final concentration of 50 mg/L. All samples were analyzed twice (two determinations in the same analytical run). Statistical analyses Statistical analysis of the data was performed using both Microsoft Office Excel (Microsoft Corporation, Redmond, WA) and Statistical Package for Social Sciences (SPSS) software package, version 15.0 for Windows (SPSS Inc., Chicago, IL). The chosen confidence level was 95%. Univariate statistical methods were used to calculate descriptive statistical parameters (mean, median, standard deviation, minimum and maximum) for each element within each kind of sample: breast milk collected after 1, 4, 8, 12 and 16 weeks of giving birth. The Kolmogorov–Smirnov normality test was applied to evaluate the distribution of each data set. The two-sample t-test was performed for comparison of means. Correlations between means were assessed by Pearson’s correlation analyses of ranks.
Results All variables under scrutiny were found to follow a normal distribution (p50.05), following application of the Kolmogorov– Smirnov test. The results obtained together with descriptive statistics are summarised in Table 3.
Trace element compositional changes in human milk
DOI: 10.3109/09637486.2014.893281
Table 3. Statistical data pertaining to oligoelements (data in mg/kg) in (human) breast milk, as a function of lactation time.
Time
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Rb
7 days 4 weeks 8 weeks 12 weeks 16 weeks Al 7 days 4 weeks 8 weeks 12 weeks 16 weeks Co 7 days 4 weeks 8 weeks 12 weeks 16 weeks Ni 7 days 4 weeks 8 weeks 12 weeks 16 weeks As 7 days 4 weeks 8 weeks 12 weeks 16 weeks Pb 7 days 4 weeks 8 weeks 12 weeks 16 weeks V 7 days 4 weeks 8 weeks 12 weeks 16 weeks Cr 7 days 4 weeks 8 weeks 12 weeks 16 weeks Mo 7 days 4 weeks 8 weeks 12 weeks 16 weeks Ba 7 days 4 weeks 8 weeks 12 weeks 16 weeks TI 7 days 4 weeks 8 weeks 12 weeks 16 weeks Be 7 days 4 weeks 8 weeks 12 weeks 16 weeks Cd 7 days 4 weeks 8 weeks 12 weeks 16 weeks
Mean
Std. Deviation
Median
Min.
Max.
891.4* 717.2* 664.5* 613.6* 579.5 133.2 107.1 77.9* 89.2 74.9 0.65 0.58 0.55 0.54 0.53 4.12 3.91 4.22 4.02 3.81 2.60* 1.98 1.85 1.53 1.62 0.15 0.14 0.060 0.18 0.26 2.56* 1.92* 1.62* 1.61* 1.51* 41.80 49.74* 37.93 35.11* 34.94 4.12 3.06 2.69 3.87 3.30 3.30* 3.42 2.53 2.72 2.12* 0.062* 0.032 0.048 0.0092 0.014* 0.024 0.056* 0.021 0.022 0.010 0.027 0.060 0.023 0.055 0.060
284.8 261.3 267.6 245.4 229.4 112.6 104.1 87.5 82.7 56.4 0.36 0.19 0.23 0.18 0.15 2.32 2.02 2.38 2.38 2.49 2.50 1.68 1.44 1.04 1.29 0.62 0.67 0.67 0.71 0.68 1.20 0.71 0.71 0.69 0.48 16.88 20.98 13.66 15.55 9.55 3.48 3.73 2.52 3.00 2.64 1.83 1.98 2.39 2.59 1.00 0.19 0.11 0.16 0.092 0.13 0.061 0.089 0.081 0.063 0.062 0.098 0.075 0.079 0.12 0.073
835.0 674.3 615.4 597.5 585.3 102.5 61.6 45.9 51.9 55.0 0.56 0.52 0.56 0.49 0.50 4.03 3.95 4.09 3.72 3.31 1.68 1.69 1.66 1.43 1.57 0.11 0.17 0.10 0.11 0.40 2.34 1.63 1.39 1.42 1.54 45.33 43.37 39.44 30.56 35.34 3.47 1.38 2.18 3.19 4.39 3.14 2.99 1.78 1.94 2.09 0.019 0.012 0.0090 0.0094 0.010 0.031 0.065 0.027 0.014 0.026 0.0044 0.050 0.024 0.031 0.050
442.6 348.5 136.2 157.6 189.6 6.9 15.2 10.7 9.3 2.3 0.25 0.35 0.24 0.29 0.31 0.13 0.44 0.72 0.51 0.055 0.52 0.11 0.44 0.23 0.42 0.93 0.91 0.87 0.85 0.92 0.69 1.12 0.087 0.82 0.72 13.84 21.78 13.19 12.68 16.89 0.040 0.49 1.10 0.18 1.82 0.49 0.13 0.039 0.38 0.49 0.103 0.097 0.081 0.117 0.132 0.093 0.10 0.11 0.099 0.11 0.081 0.026 0.12 0.079 0.044
1321.0 1315.0 1146.0 1221.0 1159.0 361.9 467.0 342.9 293.4 207.5 2.06 1.12 0.99 0.96 0.85 7.89 8.38 7.64 8.86 8.06 11.12 6.82 5.43 3.49 4.26 1.14 1.59 1.38 1.76 1.32 6.18 3.79 3.08 3.52 2.48 69.12 89.22 60.10 65.11 47.01 9.54 10.18 5.90 10.56 6.66 7.78 7.65 9.25 10.75 4.69 0.51 0.27 0.53 0.26 0.29 0.12 0.22 0.19 0.12 0.099 0.29 0.22 0.17 0.32 0.21
*Indicates significant differences from previous (4 to 8 weeks, for example) values (p50.01).
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Most measured levels of trace (essential) elements tended to decline during the first months of lactation. The decrease was especially significant for Rb, V, Ba and Tl. The exceptions were Pb and Cd, which showed a tendency for increased levels in mature milk, notwithstanding the fact that the increment did not reach statistical significance. In the case of TAS, a significant difference (p50.001) exists between the results obtained for breast milk after 7 days and 4 weeks of lactation, but not for the subsequent collection times. For Rb, significant differences (p50.001) were found between determinations until the 12th week of lactation. For V, a significant difference (p50.005) was noted between the 1st and the remaining weeks and again between the 4th and 16th week post-partum. For Ba and Tl, the decrease is significant (p50.01 and p50.05, respectively) between the 1st and 16th week postpartum, while for Be that difference (p50.01) is detected between the 4th and 12th week of lactation. In the case of Cr, there appears to be a drop in the concentration of this metal at the 12th week of lactation (p50.01) which was again found between the 4th and 12th and the 4th and 16th weeks (p50.001). For the following (essential and toxic) metals, Co, Ni, Mo, Pb and Cd, there were no significant changes along the different collection times studied. With respect to Al, significant differences were detected between the 1st and 8th weeks (p50.05) and between the 4th and 8th weeks (p50.005) of suckling. Finally, for As, the only significant differences were noted between the 1st and 8th, and between the 12th and 16th (p50.05) weeks. The analysis for TAS in the same milk samples by the RandoxÕ (RANDOX Laboratories Reagent, Antrim, UK) commercial kit has been described elsewhere (Matos et al., 2009). Correlations between TAS and mean metal concentrations along the lactation time studied, as well as amongst metals, were evaluated. Strong correlations were observed between TAS and Rb, Co, V or Tl (Pearsons’ r ¼ 0.972, 0.900, 0.900 and 0.900, respectively). No correlations whatsoever were detected with other metals. The data were also analysed as a function of age and parity of women and intake of mineral supplements. Significant differences were observed between women older (increased values) and younger than 30 years-old only for Rb (p50.005) and Ba (p50.033). Regarding parity, there appears to be a statistically meaningful increase for Rb and Ni (p50.000 and p50.012, respectively) in primipara women throughout the whole lactation timeframe under study. No differences were found for the remaining metals at any time. With respect to maternal supplementation of antioxidant vitamins or minerals, women who took these supplements showed statistically different (increased) amounts of Rb (p50.003), Mo (p50.033) and Tl (p50.001) at any lactation period within the timeframe under scrutiny. Nevertheless, for Ni and Cr there appears to be a statistically meaningful increase (p50.012 and p50.001, respectively) in women who did not get any mineral/vitamins supplements during the entire time beneath study.
Discussion This work aimed at determining the amount and variation of several oligoelements in human breast milk during the first four months of lactation, and to correlate such changes with parameters such as the mother’s age, primipara versus multipara, and supplement intake. Moreover, as the TAS of these milk samples were described in a previous paper (Matos et al., 2009), correlation with those data was also performed.
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The TAS is a lumped parameter describing the sum of the activities of all antioxidant species present in human milk (Miller et al., 1993; Ziobro & Bartosz, 2003). This antioxidant system involves not only a variety of (bio)molecules, but also some trace elements (Cu, Zn, Mn and Se) (Matos et al., 2009). In this manner, maternal supplementation with antioxidant vitamins or minerals during lactation may provide a defence mechanism to reduce oxidative stress that tends to occur during the neonatal period (Niklowitz et al., 2005). The more considerable variations in the concentration of many chemical elements take place in the passage from transition milk to mature milk, but it is widely known that milk composition also differs between women. In contrast to blood, there are no wellestablished normal values for (essential, non-essential and toxic) elements in (transitory and mature) human milk, so analysis was made essentially by comparing the acquired results with those reported in the existing literature. In this way, using published data as reference, it can be concluded that the values obtained in this research effort lie within the disclosed ranges in such published data. Our results for Co, Mo, Ni, As and Cd are in close agreement with those ranges obtained in the international collaborative WHO/IAEA study on trace element levels in human milk (0.15–1.40 mg/L, 2.12–16.36 mg/L, 4.0–16.1 mg/L, 0.24–18.9 mg/ L and 51 mg/L, respectively, for Co, Mo, Ni, As and Cd), but the mean levels of Cr and V were higher than the published limits (0.78–4.35 mg/L and 0.11–0.46 mg/L, respectively). For Pb, the mean values obtained in our study were lower than the available ¨ ru¨n et al., 2011; data (2.9–16.8 mg/L) (Krachler et al., 1998; O Parr et al., 1991; Samanta et al., 2007). The mean values for Ba in human milk, found in the scientific specialty literature, ranged from 2.8 to 5.7 mg/kg, and those for Rb ranged from 640 to 960 mg/kg. The results obtained for Be and Tl are also in agreement with data reported in the literature, ranging from 0.02 to 0.05 mg/L for Be and from 0.1 to 0.2 mg/kg to Tl (Samanta et al., 2007). The aluminum concentrations determined in this study were also similar to the values reported by other researchers (3–217 mg/L) (Nascimento et al., 2010). The results obtained in the study presented herein for metal concentrations are affected by extensive standard deviations (Table 3). Indeed, large individual differences in the excretion of (essential, non-essential and toxic) elements via human milk were also commented by several researchers (Rodrı´guez et al., 2000). Whether these variations are, or not, correlated to the nutritional status of lactating women is still a controversial matter. As can be seen from Table 3, the measured levels of elements tended to decline during the first months of lactation. The decrease was especially significant for V (essential), and for Rb, Ba and Tl (non-essential). The exceptions were Pb and Cd (the increase in these elements in mature milk did not reach statistical significance). These observations are in close agreement with those of Krachler and co-workers, who have made a longitudinal study of mothers during the 293 days following postpartum (Krachler et al., 1998). The decrease in the concentration of trace elements in human milk during the course of lactation (colostrum, transitory milk and mature milk) is well documented in the scientific literature and has been considered to be a result of a decrease in the binding capacity of the milk, due to a reduction in the concentrations of protein and fat (Almeida et al., 2008; Leotsinidis et al., 2005). Regarding essential trace elements (Co, Ni, V, Cr and Mo), it is in general established that the breast-fed infants are very conveniently protected by the maternal homeostatic mechanism. The mammary gland appears to have developed processes to regulate the concentrations of such elements in milk in order to effectively supply the infants independently of the maternal status.
Int J Food Sci Nutr, 2014; 65(5): 547–551
It is supposed that the transfer of these trace elements from blood to milk does not occur by passive diffusion but instead, by controlled transport throughout the mammary gland epithelium (Almeida et al., 2008; Domello¨f et al., 2004). With regard to toxic and non-essential trace elements (Pb, Cd, Al, As, Be, Ba and Rb), the results encountered in the scientific literature are incongruous: positive correlations, which propose a passive diffusion mechanism for their transport into milk, and non-significant correlations have equally been reported (Kazi et al., 2009). In general, there is a low level of transfer of toxic metals through milk when maternal exposure levels are low (Tuzen & Soylak, 2007). Some trace elements (which can act as redox catalysts, form part of the active site or are cofactors of antioxidant enzymes) can also act as antioxidants. A significant correlation between TAS and metal concentrations was established for Co, V, Rb and Tl, which can corroborate the role of these elements in the antioxidant defense system. Until now, such correlations are insufficiently described in the literature, and further studies can shed some light into the excretion mechanisms for these essential elements. No similar results were found, but the results described in the present work can point for further researches in this field. Variations in milk composition can occur due to a variety of factors, such as maternal trace element intake and status, maternal age, parity, residing area, family income, length of gestation and infant weight (Leotsinidis et al., 2005). Higher levels of various elements were found in younger mothers and in primipara (Frkovic et al., 1996). Our results show a significant difference for Ni and Rb concentrations between primipara when compared to women with previous children for all stages of lactation. In the case of all remaining elements, no differences were found relative to the number of previous children. Regarding to the mothers age, correlation was found only for two non-essential elements (Rb and Ba) concentrations. No correlation was found for the other trace elements concentrations. These preceding results are in line with the conclusions of several researchers, that express no marked age-related variations for different essential trace concentrations when the women studied were pooled into two age groups (under and over 30 years old) (Bocca et al., 2000). The scientific literature relating to the various factors probably affecting different metal concentrations in human milk is in general controversial. For example, Leotsinidis et al. (2005) found that maternal mineral intake affected some metal concentration in Greek lactating women, while Dommello¨f et al. (2004) did not find such differences. The low effect of mineral/vitamin intakes on essential elements levels (as Ni and Cr) was expected, as their concentration in milk is not associated with maternal mineral condition, which suggests the existence of an active transport mechanism in the mammary gland for these metals. Nevertheless, supplement consumption was positively associated with an essential (Mo) and two non-essential (Rb and Tl) elements amounts during the entire time under study. Mo was present in the supplement intake, but not Rb or Tl. It is crucial that all trace elements are contained within human milk at adequate quantities in order to ensure an appropriate development of the infant’s functions, organs and systems. The results obtained in the present research work undoubtedly will have a potential impact in the design of baby foods, by allowing production of a tailor-made human milk replacer according to the age of the infant. One limitation of our study is that only 31 of 102 initial lactating women completed the study. Besides the constraint of the decrease in the sample size, this restriction may have selected a population of mothers based on physiologic and socio-economic parameters.
DOI: 10.3109/09637486.2014.893281
The main advantage of this study was the simultaneous evaluation of the oligoelement composition of human milk along 4 months of lactation, and the influence of age, parity, intake of mineral supplements on such variation. In summary, the results presented herein for all metals studied in lactating Portuguese women were consistent with those that have been reported by other authors for both (human) transitory milk and mature milk. Nevertheless, the reliability of the different inter-element interactions and their exact meaning requires further evaluation.
Declaration of interest The authors have no conflict of interest to declare.
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Leotsinidis M, Alexopoulos A, Kostopoulou-Farri E. 2005. Toxic and essential trace elements in human milk from Greek lactating women: association with dietary habits and other factors. Chemosphere 61: 238–247. Lesniewicz A, Wroz A, Wojcik A, Zyrnicki W. 2010. Mineral and nutritional analysis of Polish infant formulas. J Food Comp Anal 23: 424–431. Li R, Darling N, Maurice E, Barker L, Grummer-Strawn LM. 2005. Breastfeeding rates in the United States by characteristics of the child, mother, or family: the 2002 National Immunization Survey. Pediatrics 115:31–37. Matos C, Moutinho C, Balca˜o V, Almeida C, Ribeiro M, Marques AF, Guerra F. 2009. Total antioxidant activity and trace elements in human milk: the first 4 months of breast-feeding. Eur Food Res Technol 230: 201–208. Miller NJ, Rice-Evans C, Davies MJ, Gopinathan V, Milner A. 1993. A novel method for measuring antioxidant capacity, and its application to monitoring the antioxidant status in neonates. Clin Sci 84:407–412. Nascimento R, Froes R, Silva N, Naveira R, Mendes D, Neto W, Bento J, Silva B. 2010. Quantification of inorganic constituints in Brazilian human milk by ICP OES Anal Lett 43:960–971. Niklowitz P, Menke T, Giffei J, Andler W. 2005. Coenzyme Q10 in maternal plasma and milk throughout early lactation. BioFactors 25: 67–72. ¨ ru¨n E, Yalc¸ ın S, Aykut O, Orhan G, Morgil G, Yurdako¨k K, Uzun R. O 2011. Breast milk lead and cadmium levels from suburban areas of Ankara. Sci Total Env 409:2467–2472. Parr RM, DeMaeyer EM, Ivengar VG, Byrne AR, Kirkbright F, Scho¨ch G, Niinisto¨ L, et al. 1991. Minor and trace elements in human milk from Guatemala, Hungary, Nigeria, Philippines, Sweden, and Zaire. Biol Trace Elem Res 29:51–75. Qian J, Chen T, Lu W, Wu S, Zhu J. 2010. Breast milk macro- and micronutrient composition in lactating mothers from suburban and urban Shanghai. J Paediatr Child Health 46:115–120. Quiles JL, Ochoa JJ, Ramirez-Tortosa MC, Linde J, Bompadre S, Battino M, Narbona E, et al. 2006. Coenzyme Q concentration and total antioxidant capacity of human milk at different stages of lactation in mothers of preterm and full-term infants. Free Rad Res 40:199–206. Rahimi E, Hashemi M, Baghbadorani Z. 2009. Determination of cadmium and lead in human milk. Int J Environ Sci Tech 6:671–676. Rodrı´guez R, Alaejos S, Romero D. 2000. Concentrations of iron, copper and zinc in human milk and powdered infant formula. Int J Food Sci Nutr 51:373–380. Samanta G, Das D, Mandal B, Chowdhury T, Chakraborti D, Ahamed A. 2007. Arsenic in the breast milk of lactating women in arsenic-affected areas of West Bengal, India and its effect on infants. J Env Sci Health Part A 42:1815–1825. Tuzen M, Soylak M. 2007. Determination of trace metals in canned fish marketed in Turkey. Food Chem 101:1378–1382. VanderJagt DJ, Okolo SN, Costanza A, Blackwell W, Glew RH. 2001. Antioxidant content of the milk of Nigerian women and the sera of their exclusively breast-fed infants. Nutr Res 21:121–128. Wappelhorst O, Ku¨hn I, Heidenreich H, Markert B. 2002. Transfer of selected elements from food into human milk. Nutrition 18: 316–322. Ziobro A, Bartosz G. 2003. A comparison of the total antioxidant capacity of some human body fluids. Cell Mol Biol Lett 8:415–419.
FOOD COMPOSITION AND ANALYSIS
Trace element compositional changes in human milk during the first four months of lactation Carla Matos1, Carla Moutinho1,2, Cristina Almeida1, Anto´nio Guerra3, and Victor Balca˜o2,4 Int J Food Sci Nutr Downloaded from informahealthcare.com by Bascom Palmer Eye Institute on 12/26/14 For personal use only.
1
Faculdade de Cieˆncias da Sau´de, Universidade Fernando Pessoa, Porto, Portugal, 2IBB – Instituto para a Biotecnologia e a Bioengenharia, Centro de Engenharia Biolo´gica, Universidade do Minho, Braga, Portugal, 3Departamento de Pediatria Faculdade de Medicina do Porto/HPI - Centro Hospitalar de Sa˜o Joa˜o, Alameda Prof. Hernaˆni Monteiro, Porto, Portugal, and 4Universidade de Sorocaba, Cidade Universita´ria, Sorocaba – SP, Brazil Abstract
Keywords
The aims of this paper were to evaluate changes in specific oligoelements in human milk during the first four months of lactation and to correlate such changes with total antioxidant status (TAS) and other parameters, such as the mother’s age, primipara versus multipara, and supplement intake. Milk samples were collected from 31 lactating women following 1, 4, 8, 12 and 16 weeks after birth. Trace levels of 13 elements were measured by inductively coupled plasma-mass spectrometry (ICP-MS). The results obtained for the oligoelements exhibited a decrease in concentration from 7 days to 4 months of breast-feeding, with exceptions. Correlations were found between TAS and Co, V, Rb and Tl. Between primipara and multipara, differences were found for Ni and Rb. Regarding the mother’s age, correlation was found for Rb and Ba (increased for mothers older than 30 years). Increased amounts of Rb, Mo and Tl at any lactation period appeared in women who took supplements.
Human milk, total antioxidant status, toxic metals, trace elements
Introduction Human milk is regarded as the ideal nutrient source for the growth and development of the infant, with unique composition characteristics, distinct from either bovine milk or infant formulae (Aycicek et al., 2006; Quiles et al., 2006). It has been reported that human milk can repress oxidative stress and oxidative DNA damage in newborn infants more effectively than infant formula which indicates that human milk contains a unique defence mechanism, which is not presented either in commercial or bovine milks (Lesniewicz et al., 2010; VanderJagt et al., 2001). Breastfed infants have reduced incidences of certain diseases, mainly neonatal sepsis, gastroenteritis, urinary and respiratory infections, and lower risk of obesity, when compared to formula-fed infants (Qian et al., 2010). It is well known that the composition of human milk is influenced by many factors and varies both within and between individuals. For example, trace element and macronutrient levels may differ with respect to the timing of delivery, maternal diet and age, parity, residing area and period of lactation (Li et al., 2005). Notwithstanding the fact that mother’s milk is seen as a perfect nutrient source for the newborn, human milk can also be a pathway of maternal excretion of toxic elements. In fact, many chemicals can be transferred from both the body reserves and the blood into the breast milk of a lactating mother. In this respect, the levels of toxic metals in milk are of significance Correspondence: Prof. Carla Matos, Grupo de Investigac¸a˜o em Bioengenharia e Quı´mica Biofarmaceˆutica, Faculdade de Cieˆncias da Sau´de, Universidade Fernando Pessoa, Prac¸a 9 de Abril n 349, P-249004 Porto, Portugal. Tel: +351-225074630. Fax: +351-225074637. E-mail: [email protected]
History Received 28 July 2013 Revised 23 January 2014 Accepted 7 February 2014 Published online 10 March 2014
(Koizumi et al., 2008; Wappelhorst et al., 2002). Cadmium, lead, arsenic and aluminium are of considerable interest due to their toxicity and widespread use (Ahamed et al., 2007; Al-Saleh et al., 2003; Garcı´a-Esquinas et al., 2011; Honda et al., 2003; Rahimi et al., 2009). The aim of this study was to determine rubidium (Rb), cobalt (Co), nickel (Ni), vanadium (V), chromium (Cr), molybdenum (Mo), barium (Ba), thallium (Tl), beryllium (Be), aluminium (Al), arsenic (As), lead (Pb) and cadmium (Cd) concentrations in the breast milk of healthy lactating women, during the first four months of lactation, who were living in Porto, Portugal, and to investigate the effect of mother’s age, parity and maternal supplementation of antioxidant vitamins or minerals on the concentration of those (essential, non-essential and toxic) elements. Since some trace elements, which can act as redox catalysts (namely, Ni, Co, Mo), may also be able to act as antioxidants, correlation between the metal concentration changes and the contents in total antioxidant status (TAS) was also evaluated.
Patients and methods Subjects This study was conducted with lactating women (n ¼ 102) who attended the Service of Obstetrics of Hospital de Sa˜o Joa˜o (HSJ) in Porto, Portugal. Healthy women who gave birth to healthy full-term infants were eligible for entry in this study. However, only women who clearly expressed the intention of exclusively breastfeeding their babies during their first 4 months of life were approached. Women were consecutively invited to participate in the study according to the criteria described hereafter. Regarding the
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Table 1. Descriptive data relating to lactating mothers (n ¼ 31) and anthropometric values of suckling babies (n ¼ 31) at 0 days after birth.
Gestational age of baby (weeks) Maternal age (years) Parity Baby weight (g) Baby length (cm) Baby HC (cm)
Mean ± SD
Amplitude (min.–max.)
39.1 ± 1.3 30.9 ± 3.9 0.6 ± 0.7 3318 ± 467 49.6 ± 1.7 34.1 ± 1.3
37.0–42.0 21–39 0–2 2525–4090 45.0–53.0 31.0–36.0
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HC ¼ Head Circumference; SD ¼ Standard Deviation.
mothers, the inclusion criteria were (i) to have had a watched over gestation, (ii) to have decided to breast-feed the baby, and (iii) to live in Porto, and the criteria for exclusion were (i) to have a pathology preventing breast-feeding (tumour, HIV carrier, hepatitis B or C carrier), (ii) to be under pharmacological therapy preventing breast-feeding, and (iii) not willing to, or prevented from, breast-feeding. Concerning the babies, the criteria for inclusion were: (i) to have an adequate weight to the gestational age, (ii) to be a term newborn (gestation equal or higher than 37 weeks), and (iii) to be exclusively breast-fed during all the study or at least during the first four months of age, while the criteria for exclusion were: (i) being a premature or preterm newborn, (ii) having pathologies or intercurrences preventing breast-feeding or that interfered with normal growth (neurological and metabolic diseases, polymalformative syndromes, congenital cardiopathies, or others preventing breast-feeding), and (iii) being term newborns but possessing inadequate weight (either low or high) for the gestational age. The study was approved by the Hospital Ethical Committee and all the participating women gave their written informed consent. One hundred and two (102) lactating women gave their consent to participate in the study after explanation of the procedures, but only thirty-one (31) completed the study. The reasons for this were several and diverse in nature: nipple discomfort, lack of milk after only a few days or weeks, reduced availability for breast-feeding. For those 31 women, all infants were exclusively breast-fed on demand for 4 months. The ages of the women ranged between 21 and 39 years old, as shown in Table 1. Milk samples Breast milk samples were collected from each breast (by either breast pump or hand expression) before and after each feed, over a 24-h period. Samples were collected several times during one day (after 1, 4, 8, 12 and 16 weeks after birth) to sterile, and tracemetals free, plastic containers, kept refrigerated at 4 C and pooled together to produce a milk sample for that day, for the analysis. Samples were homogenized and stored in a household freezer for a maximum of 24 h, until transport on ice to the research laboratory, where they were stored at 80 C until analysis was in order. Determination of trace metals Trace metals were determined by the inductively coupled plasmamass spectrometry (ICP-MS). Ultrapure water (R418 M m1) obtained through a Milli-QTM system (Millipore; Billerica, MA) was used in the preparation of all solutions. All reagents used were obtained from Fluka (Buchs SE, Switzerland) and were of analytical grade or better, except for nitric acid, which was of SuprapurÕ grade (Merck, Darmstadt, Germany). Adequately acid-washed plastic materials were used at all times to avoid contamination during sample preparation. Milk analysis was performed by using a VG Elemental (Winsford, UK), PlasmaQuad 3 ICP-MS, equipped with a
Table 2. Main instrumental and operating conditions for ICP-MS analytical equipment. Instrument parameter Detector Detection mode Acquisition mode Rf power (W) Nebuliser gas flow (L/min) Auxiliary gas flow rate (L/min) Cool gas flow (L/min) Acquisition mode Sweeps Dwell time (ms) Channels per mass Channel spacing Replicates
Condition Sequential Pulse counting Continuous 1350 0.78 0.60 13.0 Peak jumping 200 10 1 0.02 2
MeinhardÕ type A pneumatic concentric nebuliser, a quartz water cooled impact-bead spray chamber, a standard quartz tube torch and nickel sample and skimmer cones. Both the spray chamber and sampling interface were cooled down to 10 C by circulating water. Argon of 99.9999% purity (Alphagaz 2TM, supplied by Air Liquide, Maia, Portugal) was used as plasma source. For ICP-MS waste draining, a Gilson Minipuls 3 (VilliersLe Bel, France) peristaltic pump was used. The ICP-MS operation and data acquisition was accomplished by using PlasmaLabÕ software (MUSA, Waltham, MA). The main operating conditions for the ICP-MS determinations are indicated in Table 2. Samples were analysed after microwave oven (Milestone, model MLS 1200 mega, Gemini BV, Haaksbergen, The Netherlands) digestion in teflon vessels (2 g of milk added with 1 mL of 65% HNO3 and 1 mL of 30% H2O2). ICP-MS calibration solutions were prepared by dilution of commercial solutions (AccuTraceTM Reference Standard, ICPMS-200.8-CAL1R-1; Atomic Spectroscopy Standard Solution V 70008, Fluka, Buchs SE, Switzerland, for Ba; and Rubidium atomic absorption standard solution 1000 mg/mL, Sigma-Aldrich Co., St. Louis, MO, for Rb). Internal standards (Sc, Y, In, Tb and Bi) were added to the diluting solutions via dilution of a commercial aqueous solution (AccuTraceÔ Reference Standard, ICP-MS-200.8-IS-1), in order to attain a final concentration of 50 mg/L. All samples were analyzed twice (two determinations in the same analytical run). Statistical analyses Statistical analysis of the data was performed using both Microsoft Office Excel (Microsoft Corporation, Redmond, WA) and Statistical Package for Social Sciences (SPSS) software package, version 15.0 for Windows (SPSS Inc., Chicago, IL). The chosen confidence level was 95%. Univariate statistical methods were used to calculate descriptive statistical parameters (mean, median, standard deviation, minimum and maximum) for each element within each kind of sample: breast milk collected after 1, 4, 8, 12 and 16 weeks of giving birth. The Kolmogorov–Smirnov normality test was applied to evaluate the distribution of each data set. The two-sample t-test was performed for comparison of means. Correlations between means were assessed by Pearson’s correlation analyses of ranks.
Results All variables under scrutiny were found to follow a normal distribution (p50.05), following application of the Kolmogorov– Smirnov test. The results obtained together with descriptive statistics are summarised in Table 3.
Trace element compositional changes in human milk
DOI: 10.3109/09637486.2014.893281
Table 3. Statistical data pertaining to oligoelements (data in mg/kg) in (human) breast milk, as a function of lactation time.
Time
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Rb
7 days 4 weeks 8 weeks 12 weeks 16 weeks Al 7 days 4 weeks 8 weeks 12 weeks 16 weeks Co 7 days 4 weeks 8 weeks 12 weeks 16 weeks Ni 7 days 4 weeks 8 weeks 12 weeks 16 weeks As 7 days 4 weeks 8 weeks 12 weeks 16 weeks Pb 7 days 4 weeks 8 weeks 12 weeks 16 weeks V 7 days 4 weeks 8 weeks 12 weeks 16 weeks Cr 7 days 4 weeks 8 weeks 12 weeks 16 weeks Mo 7 days 4 weeks 8 weeks 12 weeks 16 weeks Ba 7 days 4 weeks 8 weeks 12 weeks 16 weeks TI 7 days 4 weeks 8 weeks 12 weeks 16 weeks Be 7 days 4 weeks 8 weeks 12 weeks 16 weeks Cd 7 days 4 weeks 8 weeks 12 weeks 16 weeks
Mean
Std. Deviation
Median
Min.
Max.
891.4* 717.2* 664.5* 613.6* 579.5 133.2 107.1 77.9* 89.2 74.9 0.65 0.58 0.55 0.54 0.53 4.12 3.91 4.22 4.02 3.81 2.60* 1.98 1.85 1.53 1.62 0.15 0.14 0.060 0.18 0.26 2.56* 1.92* 1.62* 1.61* 1.51* 41.80 49.74* 37.93 35.11* 34.94 4.12 3.06 2.69 3.87 3.30 3.30* 3.42 2.53 2.72 2.12* 0.062* 0.032 0.048 0.0092 0.014* 0.024 0.056* 0.021 0.022 0.010 0.027 0.060 0.023 0.055 0.060
284.8 261.3 267.6 245.4 229.4 112.6 104.1 87.5 82.7 56.4 0.36 0.19 0.23 0.18 0.15 2.32 2.02 2.38 2.38 2.49 2.50 1.68 1.44 1.04 1.29 0.62 0.67 0.67 0.71 0.68 1.20 0.71 0.71 0.69 0.48 16.88 20.98 13.66 15.55 9.55 3.48 3.73 2.52 3.00 2.64 1.83 1.98 2.39 2.59 1.00 0.19 0.11 0.16 0.092 0.13 0.061 0.089 0.081 0.063 0.062 0.098 0.075 0.079 0.12 0.073
835.0 674.3 615.4 597.5 585.3 102.5 61.6 45.9 51.9 55.0 0.56 0.52 0.56 0.49 0.50 4.03 3.95 4.09 3.72 3.31 1.68 1.69 1.66 1.43 1.57 0.11 0.17 0.10 0.11 0.40 2.34 1.63 1.39 1.42 1.54 45.33 43.37 39.44 30.56 35.34 3.47 1.38 2.18 3.19 4.39 3.14 2.99 1.78 1.94 2.09 0.019 0.012 0.0090 0.0094 0.010 0.031 0.065 0.027 0.014 0.026 0.0044 0.050 0.024 0.031 0.050
442.6 348.5 136.2 157.6 189.6 6.9 15.2 10.7 9.3 2.3 0.25 0.35 0.24 0.29 0.31 0.13 0.44 0.72 0.51 0.055 0.52 0.11 0.44 0.23 0.42 0.93 0.91 0.87 0.85 0.92 0.69 1.12 0.087 0.82 0.72 13.84 21.78 13.19 12.68 16.89 0.040 0.49 1.10 0.18 1.82 0.49 0.13 0.039 0.38 0.49 0.103 0.097 0.081 0.117 0.132 0.093 0.10 0.11 0.099 0.11 0.081 0.026 0.12 0.079 0.044
1321.0 1315.0 1146.0 1221.0 1159.0 361.9 467.0 342.9 293.4 207.5 2.06 1.12 0.99 0.96 0.85 7.89 8.38 7.64 8.86 8.06 11.12 6.82 5.43 3.49 4.26 1.14 1.59 1.38 1.76 1.32 6.18 3.79 3.08 3.52 2.48 69.12 89.22 60.10 65.11 47.01 9.54 10.18 5.90 10.56 6.66 7.78 7.65 9.25 10.75 4.69 0.51 0.27 0.53 0.26 0.29 0.12 0.22 0.19 0.12 0.099 0.29 0.22 0.17 0.32 0.21
*Indicates significant differences from previous (4 to 8 weeks, for example) values (p50.01).
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Most measured levels of trace (essential) elements tended to decline during the first months of lactation. The decrease was especially significant for Rb, V, Ba and Tl. The exceptions were Pb and Cd, which showed a tendency for increased levels in mature milk, notwithstanding the fact that the increment did not reach statistical significance. In the case of TAS, a significant difference (p50.001) exists between the results obtained for breast milk after 7 days and 4 weeks of lactation, but not for the subsequent collection times. For Rb, significant differences (p50.001) were found between determinations until the 12th week of lactation. For V, a significant difference (p50.005) was noted between the 1st and the remaining weeks and again between the 4th and 16th week post-partum. For Ba and Tl, the decrease is significant (p50.01 and p50.05, respectively) between the 1st and 16th week postpartum, while for Be that difference (p50.01) is detected between the 4th and 12th week of lactation. In the case of Cr, there appears to be a drop in the concentration of this metal at the 12th week of lactation (p50.01) which was again found between the 4th and 12th and the 4th and 16th weeks (p50.001). For the following (essential and toxic) metals, Co, Ni, Mo, Pb and Cd, there were no significant changes along the different collection times studied. With respect to Al, significant differences were detected between the 1st and 8th weeks (p50.05) and between the 4th and 8th weeks (p50.005) of suckling. Finally, for As, the only significant differences were noted between the 1st and 8th, and between the 12th and 16th (p50.05) weeks. The analysis for TAS in the same milk samples by the RandoxÕ (RANDOX Laboratories Reagent, Antrim, UK) commercial kit has been described elsewhere (Matos et al., 2009). Correlations between TAS and mean metal concentrations along the lactation time studied, as well as amongst metals, were evaluated. Strong correlations were observed between TAS and Rb, Co, V or Tl (Pearsons’ r ¼ 0.972, 0.900, 0.900 and 0.900, respectively). No correlations whatsoever were detected with other metals. The data were also analysed as a function of age and parity of women and intake of mineral supplements. Significant differences were observed between women older (increased values) and younger than 30 years-old only for Rb (p50.005) and Ba (p50.033). Regarding parity, there appears to be a statistically meaningful increase for Rb and Ni (p50.000 and p50.012, respectively) in primipara women throughout the whole lactation timeframe under study. No differences were found for the remaining metals at any time. With respect to maternal supplementation of antioxidant vitamins or minerals, women who took these supplements showed statistically different (increased) amounts of Rb (p50.003), Mo (p50.033) and Tl (p50.001) at any lactation period within the timeframe under scrutiny. Nevertheless, for Ni and Cr there appears to be a statistically meaningful increase (p50.012 and p50.001, respectively) in women who did not get any mineral/vitamins supplements during the entire time beneath study.
Discussion This work aimed at determining the amount and variation of several oligoelements in human breast milk during the first four months of lactation, and to correlate such changes with parameters such as the mother’s age, primipara versus multipara, and supplement intake. Moreover, as the TAS of these milk samples were described in a previous paper (Matos et al., 2009), correlation with those data was also performed.
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The TAS is a lumped parameter describing the sum of the activities of all antioxidant species present in human milk (Miller et al., 1993; Ziobro & Bartosz, 2003). This antioxidant system involves not only a variety of (bio)molecules, but also some trace elements (Cu, Zn, Mn and Se) (Matos et al., 2009). In this manner, maternal supplementation with antioxidant vitamins or minerals during lactation may provide a defence mechanism to reduce oxidative stress that tends to occur during the neonatal period (Niklowitz et al., 2005). The more considerable variations in the concentration of many chemical elements take place in the passage from transition milk to mature milk, but it is widely known that milk composition also differs between women. In contrast to blood, there are no wellestablished normal values for (essential, non-essential and toxic) elements in (transitory and mature) human milk, so analysis was made essentially by comparing the acquired results with those reported in the existing literature. In this way, using published data as reference, it can be concluded that the values obtained in this research effort lie within the disclosed ranges in such published data. Our results for Co, Mo, Ni, As and Cd are in close agreement with those ranges obtained in the international collaborative WHO/IAEA study on trace element levels in human milk (0.15–1.40 mg/L, 2.12–16.36 mg/L, 4.0–16.1 mg/L, 0.24–18.9 mg/ L and 51 mg/L, respectively, for Co, Mo, Ni, As and Cd), but the mean levels of Cr and V were higher than the published limits (0.78–4.35 mg/L and 0.11–0.46 mg/L, respectively). For Pb, the mean values obtained in our study were lower than the available ¨ ru¨n et al., 2011; data (2.9–16.8 mg/L) (Krachler et al., 1998; O Parr et al., 1991; Samanta et al., 2007). The mean values for Ba in human milk, found in the scientific specialty literature, ranged from 2.8 to 5.7 mg/kg, and those for Rb ranged from 640 to 960 mg/kg. The results obtained for Be and Tl are also in agreement with data reported in the literature, ranging from 0.02 to 0.05 mg/L for Be and from 0.1 to 0.2 mg/kg to Tl (Samanta et al., 2007). The aluminum concentrations determined in this study were also similar to the values reported by other researchers (3–217 mg/L) (Nascimento et al., 2010). The results obtained in the study presented herein for metal concentrations are affected by extensive standard deviations (Table 3). Indeed, large individual differences in the excretion of (essential, non-essential and toxic) elements via human milk were also commented by several researchers (Rodrı´guez et al., 2000). Whether these variations are, or not, correlated to the nutritional status of lactating women is still a controversial matter. As can be seen from Table 3, the measured levels of elements tended to decline during the first months of lactation. The decrease was especially significant for V (essential), and for Rb, Ba and Tl (non-essential). The exceptions were Pb and Cd (the increase in these elements in mature milk did not reach statistical significance). These observations are in close agreement with those of Krachler and co-workers, who have made a longitudinal study of mothers during the 293 days following postpartum (Krachler et al., 1998). The decrease in the concentration of trace elements in human milk during the course of lactation (colostrum, transitory milk and mature milk) is well documented in the scientific literature and has been considered to be a result of a decrease in the binding capacity of the milk, due to a reduction in the concentrations of protein and fat (Almeida et al., 2008; Leotsinidis et al., 2005). Regarding essential trace elements (Co, Ni, V, Cr and Mo), it is in general established that the breast-fed infants are very conveniently protected by the maternal homeostatic mechanism. The mammary gland appears to have developed processes to regulate the concentrations of such elements in milk in order to effectively supply the infants independently of the maternal status.
Int J Food Sci Nutr, 2014; 65(5): 547–551
It is supposed that the transfer of these trace elements from blood to milk does not occur by passive diffusion but instead, by controlled transport throughout the mammary gland epithelium (Almeida et al., 2008; Domello¨f et al., 2004). With regard to toxic and non-essential trace elements (Pb, Cd, Al, As, Be, Ba and Rb), the results encountered in the scientific literature are incongruous: positive correlations, which propose a passive diffusion mechanism for their transport into milk, and non-significant correlations have equally been reported (Kazi et al., 2009). In general, there is a low level of transfer of toxic metals through milk when maternal exposure levels are low (Tuzen & Soylak, 2007). Some trace elements (which can act as redox catalysts, form part of the active site or are cofactors of antioxidant enzymes) can also act as antioxidants. A significant correlation between TAS and metal concentrations was established for Co, V, Rb and Tl, which can corroborate the role of these elements in the antioxidant defense system. Until now, such correlations are insufficiently described in the literature, and further studies can shed some light into the excretion mechanisms for these essential elements. No similar results were found, but the results described in the present work can point for further researches in this field. Variations in milk composition can occur due to a variety of factors, such as maternal trace element intake and status, maternal age, parity, residing area, family income, length of gestation and infant weight (Leotsinidis et al., 2005). Higher levels of various elements were found in younger mothers and in primipara (Frkovic et al., 1996). Our results show a significant difference for Ni and Rb concentrations between primipara when compared to women with previous children for all stages of lactation. In the case of all remaining elements, no differences were found relative to the number of previous children. Regarding to the mothers age, correlation was found only for two non-essential elements (Rb and Ba) concentrations. No correlation was found for the other trace elements concentrations. These preceding results are in line with the conclusions of several researchers, that express no marked age-related variations for different essential trace concentrations when the women studied were pooled into two age groups (under and over 30 years old) (Bocca et al., 2000). The scientific literature relating to the various factors probably affecting different metal concentrations in human milk is in general controversial. For example, Leotsinidis et al. (2005) found that maternal mineral intake affected some metal concentration in Greek lactating women, while Dommello¨f et al. (2004) did not find such differences. The low effect of mineral/vitamin intakes on essential elements levels (as Ni and Cr) was expected, as their concentration in milk is not associated with maternal mineral condition, which suggests the existence of an active transport mechanism in the mammary gland for these metals. Nevertheless, supplement consumption was positively associated with an essential (Mo) and two non-essential (Rb and Tl) elements amounts during the entire time under study. Mo was present in the supplement intake, but not Rb or Tl. It is crucial that all trace elements are contained within human milk at adequate quantities in order to ensure an appropriate development of the infant’s functions, organs and systems. The results obtained in the present research work undoubtedly will have a potential impact in the design of baby foods, by allowing production of a tailor-made human milk replacer according to the age of the infant. One limitation of our study is that only 31 of 102 initial lactating women completed the study. Besides the constraint of the decrease in the sample size, this restriction may have selected a population of mothers based on physiologic and socio-economic parameters.
DOI: 10.3109/09637486.2014.893281
The main advantage of this study was the simultaneous evaluation of the oligoelement composition of human milk along 4 months of lactation, and the influence of age, parity, intake of mineral supplements on such variation. In summary, the results presented herein for all metals studied in lactating Portuguese women were consistent with those that have been reported by other authors for both (human) transitory milk and mature milk. Nevertheless, the reliability of the different inter-element interactions and their exact meaning requires further evaluation.
Declaration of interest The authors have no conflict of interest to declare.
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