Longitudinal study on selenium content in human milk particularly during early lactation compared to that in infant formulas and cow's milk in Japan

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.

Micronutrients in Human Milk: Analytical Methods

Exclusive breastfeeding is recommended by the WHO for the first 6 mo of life because human milk protects against gastrointestinal infections and supplies balanced and adequate nutrient contents to the infant. However, reliable data on micronutrient concentrations in human milk are sparse, especially because some micronutrients are affected by maternal diet. Microbiological and competitive protein-binding assays, nuclear magnetic resonance or inductively coupled plasma spectroscopy, and chromatographic analyses are among the methods that have been applied to human-milk micronutrient analysis. However, the validation or evaluation of analytical methods in terms of their suitability for the complex human-milk matrix has been commonly ignored in reports, even though the human-milk matrix differs vastly from blood, plasma, or urine matrixes. Thus, information on the validity, accuracy, and sensitivity of the methods is essential for the estimation of infant and maternal intake requirements to support and maintain adequate milk micronutrient concentrations for healthy infant growth and development. In this review, we summarize current knowledge on methods used for analyzing water- and fat-soluble vitamins as well as iron, copper, zinc, iodine, and selenium in human milk and their different forms in milk; the tools available for quality control and assurance; and guidance for preanalytical considerations. Finally, we recommend preferred methodologic approaches for analysis of specific milk micronutrients.

Longitudinal study on trace mineral compositions (selenium, zinc, copper, manganese) in Korean human preterm milk

We measured selenium, zinc, copper and manganese concentrations in the human milk of Korean mothers who gave birth to preterm infants, and compared these measurements with the recommended daily intakes. The samples of human milk were collected postpartum at week-1, -2, -4, -6, -8, and -12, from 67 mothers who gave birth to preterm infants (< 34 weeks, or birth weight < 1.8 kg). All samples were analyzed using atomic absorption spectrophotometry. The concentrations of selenium were 11.8 ± 0.5, 11.4 ± 0.8, 12.7 ± 0.9, 11.4 ± 0.8, 10.8 ± 0.9, and 10.5 ± 1.3 µg/L, zinc were 7.8 ± 0.5, 9.1 ± 0.8, 7.2 ± 0.9, 8.0 ± 0.8, 7.4 ± 0.9, and 6.6 ± 1.2 mg/L, copper were 506 ± 23.6, 489 ± 29.4, 384 ± 33.6, 356 ± 32.9, 303 ± 35.0, and 301 ± 48.0 µg/L and manganese were 133 ± 4.0, 127 ± 6.0, 125 ± 6.0, 123 ± 6.0, 127 ± 6.0, and 108 ± 9.0 µg/L at week-1, -2, -4, -6, -8, and -12, respectively. The concentrations of selenium and zinc meet the daily requirements but that of copper is low and of manganese exceeds daily requirements recommended by the American Academy of Pediatrics, Committee on Nutrition.

Macronutrient, mineral and trace element composition of breast milk from Japanese women

The aim of the study was to determine the concentrations of macronutrients and the mineral and trace element composition in maternal milk of Japanese women. We collected human milk samples from mothers living throughout Japan from December 1998 to September 1999, and defined as group A the 1197 samples among them that met the following conditions: breast milk of mothers who were under 40 years old, not in the habit of smoking and/or using vitamin supplements, and whose babies showed no symptoms of atopy and whose birth weights were 2.5 kg or more. We then analyzed their contents individually. We also analyzed the amino acid and free amino acid composition of the breast milk of pooled samples from various lactation stages. Large differences were found to exist among the contents of individual human milk samples. The mean contents of each component were as follows: energy, 66.3+/-13.3 kcal/100 mL; solid matter, 12.46+/-1.56 g/100 mL; ash, 0.19+/-0.06 g/100 mL; total nitrogen, 0.19+/-0.04 g/100 mL; lipids, 3.46+/-1.49 g/100 mL; carbohydrates, 7.58+/-0.77 g/100 mL; lactose, 6.44+/-0.49 g/100 mL; pH, 6.5+/-0.3; osmotic pressure, 299+/-14 mOsm/kg.H2O; chloride, 35.9+/-16.2 mg/100 mL; sodium, 13.5+/-8.7 mg/100 mL; magnesium, 2.7+/-0.9 mg/100 mL; phosphorus, 15.0+/-3.8 mg/100 mL; potassium, 47.0+/-12.1 mg/100 mL; calcium, 25.0+/-7.1 mg/100 mL; chromium, 5.9+/-4.7 microg/100 mL; manganese, 1.1+/-2.3 microg/100mL; iron, 119+/-251 microg/100 mL; copper, 35+/-21 microg/100 mL; zinc, 145+/-135 microg/100 mL; and selenium, 1.7+/-0.6 microg/100 mL. The content of each component varied greatly as the duration of lactation increased. In conclusion, it appears to be necessary to evaluate individual differences of human milk in order to perform valid research regarding infant formula.

Selenium and breast-feeding

The objective of the present review is to discuss Se nutrition during breast-feeding, encompassing environmental and maternal constitutional factors affecting breast-milk-Se metabolism and secretion. A literature search of Medline and Webofscience was used to retrieve and select papers dealing with Se and breast milk. Although Se in natural foods occurs only in organic form, breast milk responds to organic and inorganic Se in supplements. Inorganic Se (selenite, selenate), which is largely used in maternal supplements, is not detectable in breast milk. The mammary-gland regulating mechanism controls the synthesis and secretion of seleno-compounds throughout lactation, with a high total Se level in colostrum that decreases as lactation progresses. Se appears in breast milk as a component of specific seleno-proteins and seleno-amino-acids in milk proteins that are well tolerated by breast-fed infants even in high amounts. Se in breast milk occurs as glutathione peroxidase (4-32 % total Se) > selenocystamine > selenocystine > selenomethionine. The wide range of breast-milk Se concentrations depends on Se consumed in natural foods, which reflects the Se content of the soils where they are grown. Se prophylaxis, either through soil Se fertilization or maternal supplements, is effective in raising breast-milk Se concentration. In spite of wide variation, the median Se concentration from studies worldwide are 26, 18, 15, and 17 microg/l in colostrum (0-5 d), transitional milk (6-21 d), mature milk (1-3 months) and late lactation (>5 months) respectively. Se recommendations for infants are presently not achieved in 30 % of the reported breast-milk Se concentrations; nevertheless Se status is greater in breast-fed than in formula-fed infants.

Selenium status in Saudi Arabia

Selenium (Se) is a naturally occurring trace element that is essential for animal and human nutrition, but the range between dietary requirements and toxic levels is relatively narrow. In this review, we are interested in the beneficial effects of selenium and we report on a number of studies of the selenium status of different populations in Saudi Arabia. The Status reflects the geographical area inhabited by the populations. Apart from the few available studies reviewed here, no data on the human status of Se in Saudi Arabia has been obtained. A further objective of this paper is throw some the light on the direction of future studies.

Longitudinal study of the dietary selenium intake of exclusively breast-fed infants during early lactation in Korea and Japan

213 samples of human breast milk were collected from 51 healthy Korean women. Selenium content of the samples was determined by atomic absorption spectrometry with hydride generation. The selenium content of Korean milk decreased with increase of days after birth: The arithmetic mean of selenium content was higher in colostrum (< 4 days) 34 micrograms/kg (SD +/- 11, n = 44) than in transitional milk 21 micrograms/kg (SD +/- 8, n = 78) or in mature milk (> 10 days) 13 micrograms/kg (SD +/- 6, n = 91). The daily dietary selenium intake of 0-1 month aged Korean infants fed on breast milk is estimated to be around 10 micrograms per day (3 micrograms/kg body weight) regardless of days postpartum, resulting from the calculation of our selenium data and daily milk intake during early lactation. The same result on selenium intake for Japanese newborns, as well as Korean infants, is also estimated to be around 10 micrograms per day (3 micrograms/kg body weight) regardless of days postpartum.

Selenium contents of human milk and infant formulas in Spain

The selenium content of Spanish human milk samples and different milk-based and soy-based infant formulas has been estimated by using a flow injection hydride atomic absorption spectrometric method after microwave digestion of the organic matter. Mean values of 11.4 +/- 3.7 and 10.7 +/- 4.6 ng/ml for colostrum and transitional milk, 8.4 +/- 3.4 and 5.3 +/- 1.9 ng/ml for mature milk at 1 month and up to 2 months respectively, was obtained. These values are close to those reported by others authors in Europe, and lower than the ones from the US, Japan and Korea. Selenium contents of the analyzed infants' formulas ranged from 2.7 to 9.6 ng/ml and from 1.8 to 7.5 ng/ml for soy and milk-based infant formulas, respectively. The variability in selenium contents is large, although mean values are close to the ones given in other European countries. Selenium contents are not usually given on the product. The selenium intakes were estimated assuming that infants fed only human milk. The intakes ranged from 2.0 to 8.4 micrograms/day and from 3.4 to 12.9 micrograms/day for colostrum and transitional milk, respectively, and from 2.6 to 10.3 micrograms/day for mature milk at 1 month, and from 1.2 to 8.3 micrograms/day for milk up to 2 months. The analyzed infant formulas provide significantly less selenium than the 10 micrograms/day corresponding to the recommended daily allowance for infants from 0 to 6 months.

Selenium content of milk and milk products of Turkey. II

Selenium content of 1028 milk and milk products of Turkey are presented in this study. The selenium content of human milk (colostrum, transitional, and mature milk), various kinds of milk [cow, sheep, goat, buffalo, paper boxes (3%, 1.5%, 0.012% fat), bottled milk, condensed milk (10% fat), mineral added milk (1.6%), and banana, strawberry, and chocolate milk] and milk products (kefir, yogurt, Ayran, various cheese, coffee cream, ice cream, butter, margarine, milk powder, and fruit yogurt) in Turkey were determined by a spectrofluorometric method. The selenium levels of cow milks collected from 57 cities in Turkey were also determined. Selenium levels in cow milk varied with geographical location in Turkey and were found to be lowest for Van and highest for Aksaray. The results [milk (cow, sheep, goat, buffalo and human) and milks products] were compared with literature data from different countries.

Changes in the concentrations of trace elements in human milk during lactation

Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine 18 trace elements (Ba, Be, Bi, Cd, Co, Cs, Cu, La, Li, Mn, Mo, Pb, Rb, Sb, Sn, Sr, Tl, and Zn) in 55 human milk samples from 46 healthy mothers collected during lactation periods extending to 293 days after birth. Se was quantified by hydride generation atomic absorption spectrometry (HG-AAS). To test the accuracy and the precision of the analytical procedure, milk powder reference materials (BCR 063 and BCR 150) were analyzed. The results obtained by ICP-MS and HG-AAS showed good agreement with the certified values. Whenever available, trace element concentrations determined in the human milk samples were compared to reliable literature data. The concentrations of Be (< 0.05 to 0.9 microgram/kg), Bi (< 0.09 to 2.0 micrograms/kg), Cs (1.7 to 7.7 micrograms/kg), La (< 0.05 to 3.7 micrograms/kg), Rb (440 to 1,620 micrograms/kg), and Tl (< 0.08 to 0.5 microgram/kg) are the first to be reported for human milk. The concentrations of the essential trace elements Cu (p < 0.005), Mn (p < 0.05), Mo (p < 0.0005), Se (p < 0.001), and Zn (p < 0.0005) significantly decreased and the concentrations of cobalt significantly increased (p < 0.005) in human milk during the course of lactation. All concentrations for the essential trace element tin in the human milk samples were below the method detection limit of 0.3 microgram/kg. Among the not essential and toxic elements-with the exception of Ba, Pb, and Tl-the trend toward lower concentrations with continuing lactation is much less pronounced than for the essential trace elements. With the exception of Se, the daily intakes of essential trace elements of fully breast-fed infants are considerably lower than dietary recommendations.

Quantitation of taurine and selenium levels in human milk and estimated intake of taurine by breast-fed infants during the early periods of lactation

With these results we report the following: Taurine levels in human milk decreased slightly during the early lactation period. The concentration of taurine (406 +/- 174 nmol/ml) in colostrum was significantly higher than that (335 +/- 115 nmol/ml) in mature milk. Selenium content of human milk also decreased slightly during the early lactation period. The content of selenium (28.6 +/- 19.6 ng/ml) in colostrum was significantly higher than that (1 5.1 +/- 5.9 ng/ml) in mature milk. A correlation was not found between the taurine and selenium content of human milk. The intake of taurine and selenium by breast-fed infants progressively increased with days postpartum. These results were due to the significant increase in milk intake by infants. It is suggested that the taurine and selenium levels in colostrum are more concentrated than those in mature milk. However, the absolute intake of taurine and selenium by infants are higher in mature milk.

Effectiveness of microwave based digestion procedures for the demineralization of human milk and infant formulas prior to fluorometric determination of selenium

The use of two types of microwave oven, one domestic (A) and the other specially designed for laboratory (B) for microwave-based digestion, to destroy the organic matter in milk and infant formulas prior to fluorometric determination of selenium is studied in order to check their applicability and reliability. In both systems the best results were obtained using the acid mixture HNO3-H2O2, and additional treatment with perchloric acid (60%) in a Thermoblock. The application of two different microwave-based digestion procedures to infant formulas was free of interferences. In the case of human milk, it was necessary to use the standard addition method. Values obtained for detection and quantification limits, precision and accuracy of the fluorometric determination of selenium show the usefulness of both digestion procedures. The oven designed for laboratory use (B) is preferential as it permits simultaneous digestion of eight samples.