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Free natural estrogens in raw and commercial whole milk were quantitated by radioimmunoassay. The ranges of concentration of estrone, estradiol 17-beta, and estriol were 34 to 55, 4 to 14, and 9 to 31 pg/ml. Proportions of active estrogens (estrone and estradiol) in the fat phases of milk by radioactive tracer on separated milk were 80% and 65%. These findings were supported by radioimmunoassay of skim milk and butter. Equilibrium dialysis of skim milk with hydrogen 3 labeled estrogens showed that 84 to 85% of estrone and estradiol and 61 to 66% of estriol were protein bound. Whey proteins demonstrated a greater binding capacity than casein. This result was confirmed by radioimmunoassay of dry curd cottage cheese and whey. The concentrations in curd were 35, 11, and 6 pg/g. In whey they were 4, 2, and 3 pg/ml. The quantity of active estrogens in dairy products is too low to demonstrate biological activity. Butter was highest with concentrations of 539, 82, and 87 pg/g. Human colostrum demonstrated a maximum concentration of 4 to 5 ng/ml for estrone and estriol and about .5 ng/ml for estradiol. By the 5th day postpartum, they decreased to become similar to cow's milk.
Studies from our laboratory have shown that iron is better absorbed from human milk than from cow milk and that human milk can provide insufficient iron for infants during their first year. We compared iron availability from human milk with that from other formulas and determined the factors responsible for its superiority. Adults were fed 100 ml of human milk, simulated human milk, simulated human milk containing added lactoferrin, two commercial formulas containing iron, 12 mg/qt, and human milk that had been boiled. The simulated human milk resembled human milk in concentration of protein, fat, carbohydrate, iron, total minerals, calcium, and phosphorus. Iron 59 was added to each feeding and iron incorporation into RBCs was determined 14 days after each feeding. Percent iron absorption was highest from human milk and lowest from the commercial formulas. The simulated human milk supported a 9.0% absorption; addition of lactoferrin reduced this to 4.7%. Net iron absorption was 0.12 mg/liter from human milk and 0.40 and 0.37 mg/liter from the iron-enriched commercial formulas. Absorption of iron from boiled human milk was the same as from the unboiled milk. This study confirms the unique ability of human milk to promote iron absorption. Simple manipulation of the protein, fat, lactose, calcium, phosphorus, or lactoferrin content of proprietary milk did not reproduce the iron absorption demonstrated with human milk.
Human milk promotes less than optimal growth and is associated with phosphorus deficiency and decreased bone mineralization in very-low-birth-weight (VLBW) infants. In this study, the effects of feeding premature infants either human milk (HM), fortified human milk (FHM), or special premature formula (Similac Special Care [SSC]) on growth, phosphorus metabolism, and serum type I procollagen (pColl-I-C) were evaluated. Infants fed FHM exhibited a rate of weight gain and an increase in head circumference comparable with infants fed SSC and significantly greater than infants fed HM, despite the fact that both the FHM group and the HM group demonstrated biochemical evidence of phosphorus deficiency. The pColl-I-C concentrations in VLBW infants were tenfold to 20-fold greater than concentrations in normal children older than 2 years of age. The pColl-I-C levels correlated positively with weight gain and were significantly greater in the FHM and SSC groups than in the HM group. By contrast, serum alkaline phosphatase levels did not correlate with weight gain and were significantly lower in the rapidly growing SSC group than in either of the two groups with phosphorus deficiency and presumed poor bone mineralization. We conclude that the serum pColl-I-C concentration is a biochemical marker of growth in VLBW infants and may prove useful as a predictor of growth responses to various nutritional and therapeutic interventions.
Human milk contains growth modulators of potential clinical importance to the neonate. Evidence from animal and cell culture models as well as ancillary evidence about their stability and the way some of them are processed for secretion suggest they are probably physiologically significant. Their presence in human milk does not by itself establish their importance; however, it is useful to explore their potential functional roles. Growth modulators present in human milk include: EGF, NGF, certain enzymes, and taurine.
Human milk samples (n = 300) were collected during a 3-week period from 10 healthy mothers and from 10 atopic mothers, all with healthy, solely breast-fed infants. The milk samples were analysed by an enzyme-linked immunosorbent assay (ELISA) for the content of bovine beta-lactoglobulin (BLG). In a cross-over design the atopic and non-atopic mothers alternated their intake of milk between homogenized and unhomogenized milk each week. On day 7, in each week, consecutive milk samples were taken before and 4, 8, 12 and 24 hr after a single ingestion of 500 ml of homogenized or unhomogenized milk. Detectable amounts of BLG (0.9-150 micrograms/l, median value 4.2 micrograms/l) were measured in 19/20 of the mothers (95%), in 9 of 10 atopic mothers and in all 10 of 10 non-atopic mothers. No correlation was found between the type of milk preparation (homogenized or unhomogenized) and the presence of BLG or the level of BLG in human milk. A great intra-individual and inter-individual variation of BLG level was found, and no relationship was observed between BLG levels and atopic status of the mothers. The interval between ingestion of 500 ml of milk and the maximal concentration of BLG on milk-free diet varied between 4 and 24 hr, median value 8 hr. The presence of BLG in human milk is a common finding in both atopic and non-atopic mothers.
Human milk is characterized not only by a complex host defense system that prevents the colonization and proliferation of common microbial pathogens that may pervade the alimentary tract and respiratory tract of the infant but also by a paucity of inflammatory agents and an array of anti-phlogistic factors. Clinical observations support the notion that the protection provided by human milk involves not only antimicrobial factors, but also anti-inflammatory agents. The major anti-inflammatory agents include enzymes that degrade mediators of inflammation, anti-proteases, lysozyme, lactoferrin, secretory IgA and a number of antioxidants including cysteine, ascorbate, alpha-tocopherol, and beta-carotene. It is pertinent that most of these factors are either absent or poorly represented in cow's milk or other artificial feedings that substitute for breast feeding and that the attainment of adult serum levels of some of these antioxidants in early infancy is dependent upon breast feeding. It may be that the provision of these antioxidants may help to protect the recipient's developing immunologic system which is quite susceptible to oxidant damage. The absence of breast feeding will thus deprive the infant of valuable protection against common enteric-respiratory disorders and their inflammatory consequences. It should be pointed out that the protective systems in human milk including the anti-inflammatory components may not be completely delineated, and that little is known of the in vivo fate of the factors and precisely how they protect the recipient. Those questions should form the basis of important research in the next decades.
Human milk is a highly complex fluid with a nutrient balance and an array of functional properties that may promote a level of metabolic efficiency that is not attainable when a cow milk-based formula is fed. This is not a novel idea. Mitchell in 1933 proposed that the level of efficiency of energy use is determined by the nutrient "balance" in the diet. Nonetheless, difficulties remain in the attempt to reconcile the low levels of intake with established estimates of energy needs. If the amount of energy that appears necessary for growth and maintenance of a 4-month-old infant is compared with that from his or her intake of an exclusive human milk diet, the infant should have little or no energy left for activity. Do metabolic economies contribute to more efficient uses of energy for growth and maintenance in breastfed infants? Are there differences in body composition? Does more efficient use of energy occur as a result of a decrease in clinical and subclinical infections? Is efficient energy utilization accomplished by significant curtailment in activity? If an excess level of energy is consumed by bottlefed infants, what are the positive or negative short-term or long-term consequences? These questions are the focus of research in numerous laboratories. Field and clinical studies of breastfed infants and in vitro studies of human milk offer unique opportunities to understand basic mechanisms of human adaptations to nutrient intake and environmental challenges.
Human milk samples react against anti-bovine beta-lactoglobulin rabbit antibodies, as measured by a competitive radioimmunoassay. Immunoreactivity was positive even in milk from mothers consuming a diet free of cow's milk. An increase with a diet rich in cow's milk proteins was detected by immunoelectrophoresis. The human milk fraction cross-reacting with anti-bovine beta-lactoglobulin antibodies corresponds to the 20 kDa fragment from the N-terminal end of human lactoferrin. Three regions of this fragment exhibit sequence homology with a sequence contained in cow's beta-lactoglobulin (between residues 124 and 141).
Human milk and plasma samples were obtained from five healthy nursing mothers who were taking nefopam hydrochloride (60 mg four-hourly) for post-episiotomy pain. Concentrations of nefopam were quantified in milk and plasma paired samples, taken daily from birth for 5 days, by a specific paired-ion reverse phase h.p.l.c. method. Although nefopam was present in human milk in an equivalent concentration to plasma (milk: plasma ratio 1.2 +/- 0.7, mean +/- s.d.), the likely infant exposure was less than 0.05 mg kg-1 day-1 which, on a body weight basis, would be less than 3% of the maternal dose.
Human milk was investigated in regard to the presence of lymphocyte growth factors. Precipitated and dialyzed protein from mature human milk was found to exhibit interleukin-1 (IL-1) activity in the murine thymocyte proliferation assay. A mitogenic effect of milk protein was also observed in cultures of human and guinea pig thymocytes, demonstrating that the effect was not species restricted. No interleukin-2 or thymocyte growth peptide activity was found. Gel filtration chromatography on Sephadex G 150 revealed three distinct peaks of IL-1 activity, with apparent molecular weights of 14, 31 and 60 kilodaltons, respectively. Chromatofocusing showed IL-1 activity in four peaks, the major peak eluting at an isoelectric point of 5.0. Similar molecular heterogeneity has previously been demonstrated for IL-1 isolated from macrophages and other sources. The physiological role of milk-derived IL-1 is unknown, but it is proposed that it might act as an immunostimulating factor in the mammary gland, and hypothetically also in the breast-fed infant. Since IL-1 is a potent pyrogen, it is also suggested that milk-derived IL-1 contributes to the well-known pyrogenic activity of milk.
Human milk samples were collected from mothers on the third post-partum day with a manual breast-pump and pooled. They were divided into aliquots and stored at room temperature (24-25 degrees C), and at 4 degrees, 37 degrees and -20 degrees C. The creamatocrit (CR) values decreased significantly after storage at room temperature (P less than 0.03), or at 37 degrees C (P less than 0.001) for 45 min and 30 min, respectively. Creamatocrit remained stable for 14 d at 4 degrees C, and for up to 28 d at -20 degrees C. However, freezing and thawing samples twice significantly decreased creamatocrit values (P less than 0.001). The total energy concentration of the samples stored at -20 degrees C was stable for 28 d. These results indicate that strict precautions must be taken when handling and storing human milk samples for analysis of lipid content.
Human milk from 38 mothers was analysed by radioimmunological method for content of bovine beta-lactoglobulin. Detectable amounts (5-33 micrograms/l) of immunoactive beta-lactoglobulin were found in 18 human milk samples. Milk from 3 mothers, whose infants suffered from infantile colic contained high amounts of beta-lactoglobulin (32, 18 and 14 micrograms/l respectively). With the mothers on a cow's milk free diet the contents fell to non-detectable amounts in two mothers and to 6 micrograms/l in the third. All three infants became free from colic.
Unfortified human milk does not normally provide enough protein to secure maximal growth in low-body-weight (LBW) infants. Due to the practical difficulties in obtaining human milk protein (HMP), a bovine milk protein preparation (BMP) was designed by computer calculation to contain as close as possible the amino acid composition of the nutritionally available human milk proteins. Twenty-one AGA, LBW infants (BW of 1,180 to 1,600 g, GA of 27 to 33 weeks) were randomly assigned to be fed HM enriched either with HMP (9 infants) or BMP (12 infants). When full volume intake (170 ml/kg/day) was reached, the protein intakes were 3.6 +/- 0.5 and 3.3 +/- 0.3 g/kg/day, respectively, in the two diet groups. During the study period of 24 days, the infants achieved intrauterine or better weight gains: 32.9 +/- 3.3 g/day (17.7 +/- 1.9 g/kg/day) in the HMP group and 34.7 +/- 7.3 g/day (18.3 +/- 3.5 g/kg/day) in the BMP group. Serum urea nitrogen, acid-base status, and albumin values were normal and similar in both groups of infants. Plasma concentrations of total essential and total amino acids at the end of the study were 3,999 and 1,539 mumol/L and 3,899 and 1,422 mumol/L in the HMP and the BMP groups, respectively. The concentrations of all individual plasma amino acids were similar in both feeding groups. These results show that feeding human milk fortified with a modified bovine milk protein preparation produces satisfactory growth and a plasma amino acid profile similar to that found in LBW infants fed exclusively human milk protein at similar intakes.
Human milk contains factors such as IgA and lactoferrin that increase the newborn infant's resistance to infection. Preterm infants are fed pooled milk, which is normally sterilised by heating. After standard heat sterilisation IgA and lactoferrin were undetectable in milk samples. Pasteurisation also sterilised milk samples even after heavy artificial contamination and did not damage the proteins. Gamma-irradiation sterilised equally effectively but caused some denaturation of IgA and lactoferrin. Since most of the milk samples were sterile or had only light contamination with skin bacteria, there seems to be no need for routine sterilisation. If sterilisation is necessary, the method used should be chosen to minimise damage to milk proteins.
Human milk trypsin was purified by adsorption chromatography on cellulose-bound 4-aminobenzamidine; its molecular weight was about 24,000 daltons. Its concentration determined by a radioimmunoassay varies between 2.9 and 5.6 micrograms/l.
Human milk obtained from 21 American nursing mothers was studied for the presence of secretory immunoglobulin A antibody to rotavirus, the most common etiological agent of infantile gastroenteritis. Antibody was quantitated by adaptation of a recently described solid-phase radioimmunoassay technique that employs simian rotavirus as a convenient substitute antigen for human rotavirus. Of the mothers tested, 80% (12 of 15) possessed milk antibody within a week of parturition, whereas 56% of those tested (5 of 9) secreted milk antibody as late as 6 or 9 months postpartum. Specificity of the radioimmunoassay was demonstrated by absorption of antibody with purified rotavirus. Our detection by radioimmunoassay of antibody to rotavirus in milk samples collected past the colostrum stage is in contrast to other studies that have failed to detect antibody in human milk by immunofluorescence or neutralization tests. The present study also suggested that the appearance of secretory immunoglobulin A antibody in the milk of mothers previously lacking milk antibody may be correlated with subclinical infection of the mother with rotavirus.
Human milk was found to contain naturally occuring beta-, gamma- and delta-tocopherol and gamma-tocotrienol in addition to alpha-tocopherol on thin-layer chromatography. Some of the tocopherols were also identified by gas-liquid chromatography and mass spectrometry. The mean content of alpha-, beta-, gamma- and delta-tocopherol was 319.3, 7.6, 23.9 and 4.9 mug/g lipid in twelve human colostra 52.5, 1.8, 10.2 and 2.3 mug/g lipid in three transitional milks and 61.7, 2.0, 9.2 and 1.1 mug/g lipid in three normal milks, respectively. A markedly high concentration of alpha-tocopherol was found in colostrum compared with transitional and normal human milk. Gamma-Tocotrienol was detected in colostrum as only one tocotrienol derivative on thin-layer chromatography. The importance of colostrum as the source of vitamin E for the newborn is suggested.