Calcium and phosphorus in human milk

Longitudinal Changes in Human Milk Minerals and Vitamins in the Chinese Population: A Scoping Review

This scoping review aims to investigate longitudinal changes in minerals and vitamins concentrations in human milk among the Chinese population. Following the PRISMA-ScR guidelines, a comprehensive and systematic literature search was conducted using both English and Chinese databases. Data were extracted and categorized into six defined lactation stages. We found that the concentration of most minerals decreased throughout the lactation period, although calcium (Ca) and magnesium (Mg) fluctuated slightly across lactation periods. Fat-soluble vitamins also showed a decline throughout the lactation period, while water-soluble vitamins exhibited an increasing trend. However, folic acid, biotin, and pantothenic acid demonstrated a downward trend. Overall, this review has identified the longitudinal changes in minerals and vitamins concentrations in human milk among the Chinese population. In order to conduct a more in-depth examination of maternal characteristics and nutritional factors of the composition of human milk, it is recommended to utilize standardized protocols for the collection and analysis of human milk samples.

Human Milk Micronutrients and Child Growth and Body Composition in the First 2 years: A Systematic Review

Human milk (HM) provides a plethora of nutritional and non-nutritional compounds that support infant development. For many compounds, concentrations vary substantially among mothers and across lactation, and their impact on infant growth is poorly understood. We systematically searched MEDLINE, Embase, the Cochrane Library, Scopus, and Web of Science to synthesize evidence published between 1980 and 2022 on HM components and anthropometry through 2 y of age among term-born infants. Outcomes included weight-for-length, length-for-age, weight-for-age, body mass index (in kg/m2)-for-age, and growth velocity. From 9992 abstracts screened, 144 articles were included and categorized based on their reporting of HM micronutrients, macronutrients, or bioactive components. Micronutrients (vitamins and minerals) are reported here, based on 28 articles involving 2526 mother-infant dyads. Studies varied markedly in their designs, sampling times, geographic and socioeconomic settings, reporting practices, and the HM analytes and infant anthropometrics measured. Meta-analysis was not possible because data were sparse for most micronutrients. The most-studied minerals were zinc (15 articles, 1423 dyads) and calcium (7 articles, 714 dyads). HM iodine, manganese, calcium, and zinc concentrations were positively associated with several outcomes (each in ≥2 studies), whereas magnesium (in a single study) was negatively associated with linear growth during early lactation. However, few studies measured HM intake, adjusted for confounders, provided adequate information about complementary and formula feeding, or adequately described HM collection protocols. Only 4 studies (17%) had high overall quality scores. The biological functions of individual HM micronutrients are likely influenced by other HM components; yet, only 1 study analyzed data from multiple micronutrients simultaneously, and few addressed other HM components. Thus, available evidence on this topic is largely inconclusive and fails to address the complex composition of HM. High-quality research employing chronobiology and systems biology approaches is required to understand how HM components work independently and together to influence infant growth and to identify new avenues for future maternal, newborn, or infant nutritional interventions.

The Effect of Holder Pasteurization and Different Variants on Breast Milk Antioxidants

BACKGROUND

After birth, breast milk (BM) is a known essential source of antioxidants for infants. We analyzed the non-enzymatic total antioxidant capacity (TAC), oxygen radical absorbance capacity (ORAC), and glutathione, calcium, transferrin, and total protein levels of human breast milk before and after Holder pasteurization (HoP).

METHODS

The collected donor BM samples were pasteurized with HoP.

RESULTS

HoP decreased TAC (-12.6%), ORAC (-12.1%), transferrin (-98.3%), and total protein (-21.4%) levels; HoP did not influence the glutathione concentration, and it increased the total calcium (+25.5%) concentration. Mothers who gave birth via Cesarean section had significantly lower TAC in their BM. TAC and glutathione levels were elevated in the BM of mothers over the age of 30. BM produced in the summer had higher glutathione and calcium levels compared to BM produced in the winter. The glutathione concentration in term milk samples was significantly higher in the first two months of lactation compared to the period between the third and sixth months. The transferrin level of BM for female infants was significantly higher than the BM for boys, and mothers with a BMI above 30 had increased transferrin in their samples.

CONCLUSIONS

Antioxidant levels in human milk are influenced by numerous factors. Environmental and maternal factors, the postpartum age at breast milk collection, and Holder pasteurization of the milk influence the antioxidant intake of the infant.

Calcium, zinc, and vitamin D in breast milk: a systematic review and meta-analysis

BACKGROUND

Global estimates of calcium, zinc and vitamin D content in breastmilk are lacking. The objective of this systematic review was to determine the calcium, zinc, and vitamin D content in breast milk.

METHODS

A systematic search of the online databases Embase, MEDLINE, and CENTRAL was conducted in November 2022 and complemented by searches of the African Journals Online database and the LILACS database, and reference lists. Studies reporting the calcium, zinc and vitamin D content in breast milk of apparently healthy mothers and infants were included. Random effects meta-analyses were conducted. The effect of influencing factors were investigated with sub-group analyses and meta-regressions.

RESULTS

A total of 154 studies reporting on breast milk calcium were identified, with a mean calcium concentration in breast milk of 261 mg/L (95% CI: 238, 284). Calcium concentration was influenced by maternal health and decreased linearly over the duration of lactation. Calcium concentration at a specific time during lactation could be estimated with the equation: calcium concentration [mg/L] = 282 - 0.2331 ✕ number of days since birth. A total of 242 studies reporting on breast milk zinc were identified, with a mean zinc concentration of 2.57 mg/L (95% CI: 2.50, 2.65). Zinc concentration was influenced by several factors, such as maternal age, gestational age, and maternal diet. Zinc concentration started high in the first weeks post-partum followed by a rapid decrease over the first months. Zinc concentration at a specific time during lactation could be estimated with the equation: zinc concentration [mg/L] = 6 + 0.0005 ✕ days - 2.0266 ✕ log(days). A total of 43 studies reporting on breast milk vitamin D were identified, with a mean total antirachitic activity of breast milk of 58 IU/L (95% CI: 45, 70), which consisted mostly of 25OHD3, and smaller amounts of vitamin D3, 25OHD2 and vitamin D2. Vitamin D concentration showed wide variations between studies and was influenced by vitamin D supplementation, continent and season.

CONCLUSIONS

This review provides global estimates of calcium, zinc and vitamin D content in breast milk, as well as indications on changes over time and depending on influencing factors.

Association between adherence to a low carbohydrate dietary (LCD) pattern with breast milk characteristics and oxidative markers in infants' urine: a cross-sectional study

BACKGROUND

Breast milk (BM) is a dynamic fluid that varies over time and between women. The variations in BM components are most likely associated with maternal diet quality. This study aimed to assess adherence to a low carbohydrate dietary (LCD) pattern with oxidative stress markers of BM characteristics and infants' urine.

MATERIALS AND METHODS

In this cross-sectional study 350 breastfeeding mothers and their infants were recruited. BM samples were collected from mothers, and urine specimens were obtained from each infant. To evaluate LCD scores, subjects were divided into 10 deciles according to the percent of energy obtained from carbohydrates, proteins, and fats. Determination of total antioxidant activity was conducted using the ferric reducing antioxidant power (FRAP), 2, 2'-diphenyl-1-picrylhydrazyl (DPPH), thiobarbituric acid reactive substances (TBARs), and Ellman's assay. Biochemical assays of samples including calcium, total protein, and triglyceride level were also performed using commercial kits.

RESULTS

Participants with the greatest LCD pattern adherence were placed into the last quartile (Q4), and those with the minimum LCD were in the first quartile (Q1). Individuals in the highest LCD quartile had significantly higher levels of milk FRAP, thiol, and protein, as well as infant urinary FRAP and lower milk MDA levels than those in the lowest quartile. Multivariate linear regression analyses indicated that higher score of the LCD pattern was associated with a higher level of milk thiol, protein, and lower level of milk MDA (p < 0.05).

CONCLUSION

Our findings show that adherence to a LCD, as defined by a low level of carbohydrates in daily food intake, is linked with improved BM quality and markers of oxidative stress in infant urine.

On the Application of Calcium Phosphate Micro- and Nanoparticles as Food Additive

The human body needs calcium and phosphate as essential nutrients to grow bones and teeth, but they are also necessary for many other biochemical purposes (e.g., the biosynthesis of phospholipids, adenosine triphosphate, ATP, or DNA). The use of solid calcium phosphate in particle form as a food additive is reviewed and discussed in terms of bioavailability and its safety after ingestion. The fact that all calcium phosphates, such as hydroxyapatite and tricalcium phosphate, are soluble in the acidic environment of the stomach, regardless of the particle size or phase, means that they are present as dissolved ions after passing through the stomach. These dissolved ions cannot be distinguished from a mixture of calcium and phosphate ions that were ingested separately, e.g., from cheese or milk together with soft drinks or meat. Milk, including human breast milk, is a natural source of calcium and phosphate in which calcium phosphate is present as nanoscopic clusters (nanoparticles) inside casein (protein) micelles. It is concluded that calcium phosphates are generally safe as food additives, also in baby formula.

Potential Applications of Endo-β-N-Acetylglucosaminidases From Bifidobacterium longum Subspecies infantis in Designing Value-Added, Next-Generation Infant Formulas

Human milk is the optimal source of infant nutrition. Among many other health benefits, human milk can stimulate the development of a Bifidobacterium-rich microbiome through human milk oligosaccharides (HMOs). In recent years, the development of novel formulas has placed particular focus on incorporating some of the beneficial functional properties of human milk. These include adding specific glycans aimed to selectively stimulate the growth of Bifidobacterium. However, the bifidogenicity of human milk remains unparalleled. Dietary N-glycans are carbohydrate structures conjugated to a wide variety of glycoproteins. These glycans have a remarkable structural similarity to HMOs and, when released, show a strong bifidogenic effect. This review discusses the biocatalytic potential of the endo-β-N-acetylglucosaminidase enzyme (EndoBI-1) from Bifidobacterium longum subspecies infantis (B. infantis), in releasing N-glycans inherently present in infant formula as means to increase the bifidogenicity of infant formula. Finally, the potential implications for protein deglycosylation with EndoBI-1 in the development of value added, next-generation formulas are discussed from a technical perspective.

Structure and elemental composition of Ceftriaxone induced pediatric nephrolithiasis

Ceftriaxone is a widely used antibiotic because to its broad-spectrum gram-negative coverage, safety, and biological half life (5-9 h) permit dose once-daily administration. It is specifically used in pediatric patients in developing countries. Ceftriaxone forms insoluble sludge/stone when combined with calcium in the urinary system. In this study, Ceftriaxone induced sludge/stones from pediatric patients were collected to identify its microstructure and composition to gather insights into the mechanism of Ceftriaxone induced sludge/stone formation. The results illustrated that Ceftriaxone induced stones formed rapidly following antibiotic administration. Ceftriaxone calcium salt crystals could easily be broken with minimal intervention. However, Ceftriaxone combined with calcium phosphate formed an insoluble stone aggregate.

Investigation of amino acids and minerals in Chinese breast milk

BACKGROUND

The nutrients in human milk, particularly amino acids and minerals, are important for infant growth and development. Since there are few reports of amino acids and minerals in Chinese breast milk, we conducted this study to establish a representative preliminary database of breast milk nutrients in Chinese breast milk. In this study, we collected breast milk from healthy mothers in seven cities in western, southern and central China. The composition, content and proportion of total amino acids and ten elements (potassium, sodium, calcium, magnesium, iron, zinc, manganese, copper, selenium and phosphorus) in human milk in different lactation stages were investigated.

RESULTS

In this study, it was found that the content of total essential amino acids (671.47 mg 100 mL^-1 ) in Chinese breast milk was higher compared with the European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) (574 mg 100 mL^-1 ), but the content of leucine (LEU) (129.01 mg 100 mL^-1 ) and cysteine (CYS) (20.31 mg 100 mL^-1 ) was much lower than that recommended by ESPGHAN. Moreover, it was found that the content of most of these ten elements decreased during lactation, and the content of calcium in Chinese breast milk was lower compared with ESPGHAN. In addition, the content of selenium (7.23-20.55 mg 1000 mL^-1 ) in breast milk from the three cities Nanchang, Shanghai and Guangzhou in China was much higher than that recommended by ESPGHAN.

CONCLUSIONS

In a word, amino acids and minerals in Chinese human milk showed a significant difference from other countries. Human milk meal or infant food should be regulated to meet the requirements of the infant and to maintain the balance of the amino acids and minerals. © 2020 Society of Chemical Industry.

Association between Breast Milk Mineral Content and Maternal Adherence to Healthy Dietary Patterns in Spain: A Transversal Study

The composition of breast milk is influenced by many factors, some of which dependent on the mother and others on the child. Changes in lactation and other factors depending on the mother's physiology and anthropometric characteristics, as well as her nutritional status and diet, are of key importance. Breast milk minerals have been extensively studied with highly uneven results. In this work, a comparison will made with data across the world. To understand the factors that might explain the disparity, several minerals (Na, K, Ca, P, Mg, Fe, Se and I) have been analyzed using ICP-MS in a set of human milk samples (n = 75). The samples had an identical geographical origin (Galicia, in northwestern Spain) but different lactation circumstances, including maternal anthropometric data, lactating time, newborn sex and maternal adherence to healthy dietary patterns (Mediterranean Diet, MD, or Atlantic Diet, AD). The required concentrations of essential elements reported in the literature are similar to those found in these Spanish women. A univariate approach revealed that factors such as lactating time, body mass index (BMI) and newborn sex have a significant influence in breastmilk mineral content. According to multivariate linear regression analysis, minerals in milk are particularly associated with lactating time, but also with newborn sex, maternal BMI, age and diet pattern in some cases. More precisely, these results suggest that the iron and selenium concentrations in the milk of Galician donors may be positively influenced by maternal adherence to AD and MD, respectively.

Human Milk Composition and Dietary Intakes of Breastfeeding Women of Different Ethnicity from the Manawatu-Wanganui Region of New Zealand

Human milk is nutrient rich, complex in its composition, and is key to a baby’s health through its role in nutrition, gastrointestinal tract and immune development. Seventy-eight mothers (19–42 years of age) of Asian, Māori, Pacific Island, or of European ethnicity living in Manawatu-Wanganui, New Zealand (NZ) completed the study. The women provided three breast milk samples over a one-week period (6–8 weeks postpartum), completed a three-day food diary and provided information regarding their pregnancy and lactation experiences. The breast milk samples were analyzed for protein, fat, fatty acid profile, ash, selected minerals (calcium, magnesium, selenium, zinc), and carbohydrates. Breast milk nutrient profiles showed no significant differences between the mothers of different ethnicities in their macronutrient (protein, fat, carbohydrate, and moisture) content. The breast milk of Asian mothers contained significantly higher levels of polyunsaturated fatty acids (PUFAs), omega-3 (n-3) and omega-6 (n-6) fatty acids, docosahexaenoic acid (DHA), and linoleic acids. Arachidonic acid was significantly lower in the breast milk of Māori and Pacific Island women. Dietary intakes of protein, total energy, saturated and polyunsaturated fat, calcium, phosphorus, zinc, iodine, vitamin A equivalents, and folate differed between the ethnic groups, as well as the number of serves of dairy foods, chicken, and legumes. No strong correlations between dietary nutrients and breast milk components were found.

Overview of Nutrients in Human Milk

The WHO recommends exclusive breastfeeding for the first 6 mo of life to promote optimal infant health and development. Understanding the micro- and macronutrient concentrations of human milk and how each nutrient fluctuates with lactational stage, maternal factors, and supplementation is imperative for supporting good breastfeeding practices. Where maternal undernutrition compromises human milk quality, a thorough awareness of the effectiveness of interventions can direct efforts to achieve both maternal and infant nutrient sufficiency. This review of current knowledge covers trends in nutrient concentrations over the course of lactation and describes the influence of maternal intake, status, supplementation, and other factors on human milk concentrations of each nutrient.

Concentrations of trace elements in human milk: Comparisons among women in Argentina, Namibia, Poland, and the United States

Human milk contains essential micronutrients for growth and development during early life. Environmental pollutants, such as potentially toxic metals, can also be transferred to the infant through human milk. These elements have been well-studied, but changing diets and environments and advances in laboratory technology require re-examining these elements in a variety of settings. The aim of this study was to characterize the concentrations of essential and toxic metals in human milk from four diverse populations. Human milk samples (n = 70) were collected in Argentina (n = 21), Namibia (n = 6), Poland (n = 23), and the United States (n = 20) using a standardized mid-feed collection procedure. Milk concentrations of calcium, zinc, iron, copper, manganese, lead, arsenic, and cadmium were determined using inductively coupled plasma mass spectrometry (ICP-MS). We used standard multiple linear regression models to evaluate differences among populations, while including infant age, infant sex, and maternal parity status (multiparous or primiparous) as covariates. Concentrations of all elements, except zinc, varied across populations after controlling for infant age, infant sex, and maternal parity. Calcium and magnesium showed more differences across populations than iron or copper. There were no significant differences among population in zinc concentrations. Mean concentrations of lead, but not arsenic, were low compared to recently published values from other populations. The concentrations of trace elements in human milk are variable among populations. Limitations due to small sample sizes and environmental contamination of some samples prevent us from drawing robust conclusions about the causes of these differences.

Is additional oral phosphate supplementation for preterm infants necessary: an assessment of clinical audit

Adequate phosphate intake is important for the prevention of metabolic bone disease in preterm infants. The European Society for Paediatric Gastroenterology, Hepatology and Nutrition recommends a daily phosphate intake of 184-230 mg/kg/day, which should be met by standard feed volumes of either commercially fortified breast milk or preterm formulae. We sought to investigate whether our local practise of providing supplemental oral phosphate for all infants born before 32 weeks' gestation continues to be necessary. Details of parenteral and milk feeding and both oral and parenteral phosphate supplementation from birth until 8 weeks of age were collected retrospectively from the case notes of 31 preterm infants. Routinely collected biochemical markers of bone mineral status were also recorded. Mean (SD) plasma phosphate concentration was higher when oral phosphate supplementation was given [2.10 (0.38) versus 1.92(0.50) mM/L without supplement (p < 0.001)]. A minimum average phosphate intake of 184 mg/kg/day was achieved by 47 and 77 % of babies in weeks 1 and 2, respectively, and by 84-100 % of infants from week 3. The percentage of plasma phosphate measurements below the minimum target of 1.8 mM/L was greater amongst unsupplemented babies (45 versus 18 %).

CONCLUSION

A majority of infants <32 weeks' gestation did not achieve the recommended phosphate intake during the first week of life. Despite achieving the recommended phosphate intake from week 3, many infants did not have plasma phosphate concentrations within the accepted normal range. Additional oral supplementation may help to achieve blood phosphate concentrations within this target range.

The nutritive and immunoprotective quality of human milk beyond 1 year postpartum: are lactation-duration-based donor exclusions justified?

Donor human milk is critical for the fragile preterm infant who does not have access to his or her mother's milk, improving survival rates and quality of survival and decreasing hospital stay. Despite the opening of donor milk banks around the world, shortages continue as demand for donor milk exceeds supply. One potential means of increasing supply is by reducing exclusion criteria that prohibit mothers from donating milk based on duration of lactation. Minimal research has been done on the composition of human milk during the second year of lactation, with most research focusing on the nutritive compounds and not the immunoprotective compounds. Several immunoprotective compounds, including lysozyme, lactoferrin, secretory immunoglobulin A, and oligosaccharides, are abundant in human milk compared to bovine-based infant formula and are partially or fully retained during Holder pasteurization, making them an important differentiating feature of donor milk. A PubMed search was conducted to review studies in human milk composition during the second year of lactation. Limitations of existing research include sample collection protocols, small study sizes, and use of populations that may have been at risk for nutritional deficiencies. Stable concentrations of several components were reported including protein, lactose, iron, copper, lactoferrin, and secretory immunoglobulin A. Lysozyme concentration increased during extended lactation, while zinc and calcium concentrations declined into the second year. Conflicting findings were reported on fat content, and no information was available regarding oligosaccharide content. More research is needed to create evidence-based guidelines regarding the nutritive and immunoprotective value of donor milk throughout the course of lactation.

Daughter dearest: Sex-biased calcium in mother's milk among rhesus macaques

Mother's milk provides building blocks necessary for infant development and growth postnatally. Minerals in milk are particularly important for infant skeletal development and may reflect maternal characteristics that are associated with the capacity to synthesize milk and sex-specific developmental priorities of the infant. Using a large sample of mother-infant dyads assigned to the outdoor breeding colony at the California National Primate Research Center (N=104), we investigated the relationship of milk calcium (Ca) and phosphorus (P) concentrations and the ratio of Ca/P to maternal and infant characteristics and to other milk variables. Ca and P are largely associated with casein micelles, and as expected, both Ca and P were positively correlated with protein concentrations in milk. Neither Ca nor P concentrations were associated with maternal parity. Mothers rearing daughters tended to produce higher mean Ca concentration in milk, and consequently a higher Ca/P ratio, than did mothers rearing sons, even though protein concentration was not elevated. These results suggest that the Ca/P ratio in rhesus milk may have been under separate selective pressure from protein content to facilitate the accelerated rate of skeletal calcification that has been observed in female Macaca mulatta infants.

Changes in trace elements during lactation in a marine top predator, the grey seal

Lactation in pinnipeds represents the most significant cost to mothers during the reproductive cycle. Dynamics of trace elements and their mobilization associated with energy reserves during such an intense physiological process remains poorly understood in marine mammals. The changes in tissue concentrations of 11 elements (Ca, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Se, V, and Zn) were investigated in a longitudinal study during the lactation period and during the post-weaning fast period. Blood, milk, blubber, and hair samples were collected sequentially from 21 mother-pup pairs of grey seals (Halichoerus grypus) from the Isle of May in Scotland. Maternal transfer through the milk was observed for all trace elements, except for Cd. As an indicator of the placental transfer, levels in pup lanugo (natal coat) revealed also the existence of maternal transfer and accumulation of all assayed trace elements during the foetal development. The placental and mammary barriers against non-essential metal transfer to offspring appear to be absent or weak in grey seals. Examining the contamination levels showed that this grey seal population seems more highly exposed to Pb than other phocid populations (2.2 mg/kg dw of grey seal hair). In contrast, blood and hair levels reflected a lower Hg exposure in grey seals from the Isle of May than in harbour seals from the southeastern North Sea. This study also showed that trace element concentrations in blood and blubber could change rapidly over the lactation period. Such physiological processes must be considered carefully during biomonitoring of trace elements, and potential impacts that rapid fluctuations in concentrations can exert on seal health should be further investigated.

Mercury and lead during breast-feeding

Hg and Pb are of public health concern due to their toxic effects on vulnerable fetuses, persistence in pregnant and breast-feeding mothers, and widespread occurrence in the environment. To diminish maternal and infant exposure to Hg and Pb, it is necessary to establish guidelines based on an understanding of the environmental occurrence of these metals and the manner in which they reach the developing human organism. In the present review, environmental exposure, acquisition and storage of these metals via maternal–infant interaction are systematically presented. Though Hg and Pb are dispersed throughout the environment, the risk of exposure to infants is primarily influenced by maternal dietary habits, metal speciation and interaction with nutritional status. Hg and Pb possess similar adverse effects on the central nervous system, but they have environmental and metabolic differences that modulate their toxicity and neurobehavioural outcome in infant exposure during fetal development. Hg is mainly found in protein matrices of animal flesh (especially fish and shellfish), whereas Pb is mainly found in osseous structures. The potential of maternal acquisition is higher and lasts longer for Pb than for Hg. Pb stored in bone has a longer half-life than monomethyl-mercury acquired from fish. Both metals appear in breast milk as a fraction of the levels found in maternal blood supplied to the fetus during gestation. Habitual diets consumed by lactating mothers pose no health hazard to breast-fed infants. Instead, cows' milk-based formulas pose a greater risk of infant exposure to neurotoxic substances.

Magnesium in human milk

Reported concentrations for magnesium in breast milk vary over a wide range (15 to 64 mg/L) with a median value of 31 mg/L and 75% of reported mean concentrations below 35 mg/L. Constitutional variables such as adolescent motherhood, gestation length, maternal undernutrition, metabolic disorders (diabetes, galactosemia), race, stage of lactation, sampling techniques (foremilk and hindmilk), as well as environmental variables such as socio-cultural diversity, smoking habits, dietary calcium and magnesium (including supplementation), vegetarianism, calciotropic agents (immunoreactive calcitonin, vitamin D), medication (hormonal contraceptives, magnesium sulfate) are critically reviewed in relation to changes in milk magnesium concentrations. Magnesium secretion into breast milk does not seem to be affected by the studied variables.

Iron and copper in human milk

The reported concentrations of iron and copper in breast milk show a wide variation. Research published over the past 50 y has reported median values of 0.47 and 0.32 mg/L for iron and copper, respectively. The levels of both metals decrease with the progress of lactation. The calculated iron-to-copper ratio of reported means differs from 0.25 to 6.29 (median = 1.18). Maternal constitutional variables such as undernutrition, iron and copper body reserves, stage of lactation, adolescent motherhood, gestation length, and infection and environmental variables such as iron and copper dietary intake, in addition to supplementation, smoking, vegetarianism, and prolonged use of hormonal contraceptives before and during lactation did not consistently affect the concentrations of iron and copper in breast milk. Extreme cases of either low or high levels of body metal availability or altered metabolism due to chelating therapy or illnesses such as Wilson's disease and infections did not affect metal transfer from blood serum to breast milk. There is no clinical or scientific support for the need of extra iron or copper, besides the quantities provided by milk in the full-term breast-fed infant, at least during the first 6 mo.