The widespread availability of safe, easily prepared artifical infant formulas has led to a marked decrease in breast feeding in industrialized societies.1 In addition, there has even been a decrease in the incidence of breast feeding in preindustrial societies.2 Recently, there has been an upsurge in interest in the value of breast feeding. It is felt by many that human milk is nutritionally superior to modified cow's milk formulas, even to the "humanized varieties."3'4 Human milk is thought to provide a degree of immunologic protection to the neonate not available in cow's milk.2'5,6 Premature infants fed human milk may have a lower incidence of necrotizing enterocolitis than those fed artificial formulas.7 Obesity and allergies may occur with a greater degree of frequency in artificially fed than in breastfed infants.4,6,8,9 Breast feeding probably enhances maternal-infant bonding processes, especially when it is instituted immediately after delivery.9,10 In preindustrial countries, breast feeding is an effective means of population control and is associated with a decreased infant mortality, when compared with artificially fed infants.11
On the negative side, there is some evidence that in very small premature infants, human-milk feedings are associated with decreased rates of linear and head growth.12*14 Both environmental pollutants and drugs ingested by the mother may be transmitted to the infant by breast milk.15,16 "Breast milk jaundice," possibly due to the presence of one or more inhibitory substances found in human milk, is relatively uncommon and is generally benign and self-limited.17
Advantages and disadvantages of breast feeding are summarized in Table 1 . Each will be discussed in turn.
Although human and cow's milk are almost isocaloric, their protein content differs both qualitatively and quantitatively, with quantitative differences in carbohydrate and mineral content (Table 2). While the fat concentration of the two is about equal (but usually slightly higher on the average in human milk), there are significant differences in the types of fat found.
There is considerable variation in the nutrient and mineral content of breast milk among different women. In addition, the constituents of breast milk may vary in the same individual, especially at different times of the day. Maternal nutrition plays an important role in regulating the concentration of the various contituents of breast milk.
Although artificial formulas have been developed to simulate human milk, many differences still remain.
Protein. The protein content of cow's milk is approximately 3.5 per cent, as against about 1 per cent in human milk, with the concentration ranging from about 1.5 to 3 percent in artificial formulas. Casein, which forms a relatively hard curd when it comes in contact with hydrochloric acid in the infant's stomach, is the predominant protein of cow's milk (about 80 per cent), while whey proteins (mostly alpha-lactalbumin and lactoferrin) comprise about 70 per cent of the protein of human milk. Some of the humanized "artificial" formulas have a whey:casein ratio similar to that of human milk.
Cow's milk contains higher concentrations of the amino acids tyrosine and phenylalanine than human milk.18,19 High serum concentrations of these amino acids may have an adverse effect on the developing central nervous system. While human milk concentrations of the sulfur-containing amino acids cystine and methionine are about equal, cow's milk has a methionine: cystine ratio of more than 3:1.18,20 Since premature infants have a deficiency of the liver enzyme cystathionase, methionine cannot be converted into cystine in these infants, with subsequent deleterious effects on the central nervous system. The amino acid taurine, present in human milk, is absent in cow's milk. There is some evidence that this substance may be a major neurotransmitter, necessary for optimal brain growth.20
ADVANTAGES AND DISADVANTAGES OF BREAST FEEDING
COMPOSITION (APPROXIMATE) OF HUMAN MILK, COW'S MILK, AND SEVERAL PROPRIETARY FORMULAS (PER 100 ML.)
Carbohydrates. The major source of carbohydrate in both cow's milk and human milk is the disaccharide lactose. While cow's milk has a lactose content of about 4.8 per cent, the content in human milk is about 6.8 per cent. Lactose is added to most of the artificial formulas to make them similar in this respect to human milk. Other carbohydrates present in small quantities in human milk appear to promote growth of Lactobacillus bifidus, the predominant microorganism of the gastrointestinal tract of breast-fed infants.
Fats. Human milk has a slightly higher' concentration of fat than cow's milk, with an increased fat content observed in human milk both early in the morning and at the end of feedings. While cow's milk contains predominantly saturated fatty acids, the major constituents of human milk are the more absorbable unsaturated fatty acids, such as oleic and linoleic acid. Vegetable oils containing linoleic acid have been added to many artificial formulas in order to simulate human milk.
The higher content of cholesterol in human milk than in cow's milk may be of biologic importance in establishing mechanisms for optimal cholesterol metabolism in later life. Lipases, which are present in higher concentrations in human than in cow's milk, may be at least partly responsible for the enhanced absorption of fat in breast-fed infants.21
Minerals. The concentration of calcium, sodium, potassium, and chloride in cow's milk is about three times greater than that in human milk, while the concentration of phosphorous is six to seven times greater. This latter phenomenon is due to the high phosphorus content of casein, the predominant protein of cow's milk. The low mineral content of human milk is advantageous during the neonatal period, since the kidney is incapable of handling a high solute load. The high concentration of phosphorus in cow's milk may lead to neonatal hypocalcemia. Although the mineral content of artificial formulas is significantly lower than that of cow's milk, none of the formulas has a mineral content as low as that of human milk.
The iron content of human milk is lower than that of cow's milk, but breast-fed infants rarely develop iron-deficiency anemia.22 This is thought to be due to the greater absorption of iron from human milk. The reason for this is not fully understood but may be related to the high lactose and vitamin C and low phosphorus content of human milk.
Zinc is present in about equal concentrations in human and cow's milk. Zincdeficiency states, such as acrodermatitis enteropathica, are, however, rarely observed in breast-fed infants.
Vitamins. Human milk supplies most of the vitamin requirements for the normal full-term infant. However, because of its low content of vitamin K, intramuscular administration of this substance following delivery is necessary for prevention of hemorrhagic disease of the newborn. Routine oral administration of vitamin D is necessary for the prevention of rickets.
RELATION TO OBESITY
There is evidence that obesity is a less common finding in breast-fed than in bottlefed infants. This may be due to one or more reasons. Breast-fed infants will usually stop sucking when their nutritional requirements are met. The high fat concentration present in human milk at the end of a feeding may act as an appetite suppressant. Bottle-fed infants are often expected to finish all the formula present in a bottle; this can lead to overfeeding and excessive weight gain. Another factor may be that infants fed artificial formulas have an increased serum osmolarity, leading to excessive thirst and a consequent desire to drink more formula than is nutritionally required.
There is a growing body of evidence that breast-fed infants are less susceptible to respiratory and gastrointestinal infections, otitis media, Escherichia coli sepsis, meningitis, staphylococcal disease, and necrotizing entercolitis.1,5"7'23'24 It is likely that the higher infant mortality observed today among artificially fed than among breast-fed infants in preindustrial countries is due in large part to the lack of immunologic factors in artificial formulas.
Both cellular and noncellular elements are responsible for these properties (Table 3). Experimentally, colostrum confers protection against rotavirus-induced gastroenteritis. In view of the substantial prevalence of this pathogen, this is potentially a very significant observation.25
Cellular elements. The predominant cell in human milk is the macrophage. Lactoferrin, lysozyme, interferon, complement (C3 and C4), and immunoglobulins are among the substances of immunologic significance found in breast milk. T-cell and B-cell lymphocytes are present in lesser numbers. The former appear to produce such substances as transfer factors, which are absorbed through the gastrointestinal tract of the newborn infant, while B-cell lymphocytes produce immunoglobulins, primarily of the secretory IgA variety.
Standard sterilization and freezing of human milk (for future use, especially in premature infants) may lead to destruction of cellular elements.26 However, macrophages may remain viable after pasteurization at 62.5°C. for 30 minutes. Since macrophages adhere to glass, collection of breast milk in glass containers may lead to attenuation of its immunologic properties.
Noncellular elements. There is growing evidence that secretory IgA plays a significant role in prevention of infection in newborn infants. This substance, which is relatively thermostable and resistant to chemical degradation, is thought to be active against viral and bacterial pathogens present in the neonatal gastrointestinal tract.
Lactoferrin is present in significantly higher concentrations in human than in cow's milk. In its unsaturated state, this iron-binding protein appears to inhibit the growth of bacterial gastrointestinal pathogens by competing for the iron necessary for their metabolism.
IMMUNOLOGIC PROPERTIES OF HUMAN MILK
Lysozyme is also found in higher concentrations in human than in cow's milk. It probably exerts its antibacterial properties through potentiation of immunoglobulin activity.
The predominance of Lactobacillus bifidus in the gastrointestinal tracts of breast-fed infants inhibits the growth of such potentially pathogenic organisms as E. coli and Shigella. These bacteria grow more readily in the mixed flora of the gastrointestinal tracts of artificially fed infants than in those of breastfed infants.
Necrotizing enterocolitis. There is suggestive evidence that premature infants fed breast milk are less susceptible to necrotizing enterocolitis than are formula-fed infants. While the pathogenesis of this disorder is not fully understood, it is felt that both small-bowel ischemia and gram-negative bacteria (primarily E. coli) play important roles. It has been postulated that macrophages present in breast milk play a significant role in the prevention of this disorder.7
Exposure of the neonatal gastrointestinal tract to cow's milk protein may lead to absorption of intact antigens and predispose the infant to such allergic disorders as atopic eczema and bronchial asthma, especially if there is a strong family history of allergies. Since solid feedings are usually introduced into the diets of artificially fed infants at an earlier age than that of breast-fed infants, the former group may be at increased risk of exposure to a variety of potentially antigenic substances.
OTHER ADVANTAGES OF BREAST FEEDING
Among the additional advantages of breast feeding are its effects on prevention of too many pregnancies in rapid succession, its transmission of thyroid hormone, and the part it plays in maternal-infant bonding.
Effect on ovulation. Prolonged breast feeding suppresses ovulation, thereby acting as the primary method of population control in areas where artificial methods of contraception are not widely utilized. Substitution of formula feeding for breast feeding thus could lead to a significant increase in the birth rate in preindustrial societies, unless or until contemporary contraceptive techniques come into widespread use.11
The infant mortality rate has increased in countries like India, Chile, and Guatemala among infants fed artificially. This may be due to suboptimal nutrition, contamination of artificial feedings, and the fact that the artificially fed infant does not receive the immunity conferred by breast milk.
Thyroid hormone. Thyroid hormones - predominantly triiodothyronine (T3) - are secreted in breast milk. The highest concentrations are observed after seven days following onset of lactation. This may be of value in prevention of brain damage in neonates with undetected hypothyroidism.27 It has been shown that the concentration of thyroxine (T4) declines and T3 rises within 48 hours of life in breast milk.28 In fact, T4 levels may be undetectable in most samples of breast milk and T3 levels so low that only 2.1-2.6 /xg. would be provided daily, as against the 18.8-25.0 µg. per day recommended for the treatment of hypothyroidism.27
Maternal-infant bonding. Breast feeding enhances the development of maternal-infant bonding. Allowing the newborn infant to nurse as soon as possible after delivery permits early eye and skin contact between mother and infant. This may be of importance in both the long-term psychologic and biologic development of the infant.
DISADVANTAGES OF BREAST FEEDING
While the advantages of breast feeding greatly outweigh those of artificial feeding, certain disadvantages, both immediate and potential, deserve mentioning. The major pitfall to breast feeding is trying to persuade a woman who is poorly motivated and psychologically unprepared to nurse her infant. In addition, there are certain other situations where breast feeding may be disadvantageous. In certain ethnic groups the capacity of breast milk to inhibit hepatic glucuronyl transferase is especially pronounced. Breast-fed Alaskan Eskimo infants have higher bilirubin levels than those who are bottle-fed, partially reflecting this characteristic.30 However, this ethnic group, like Orientals and American Indians, have higher levels than blacks and whites, regardless of the type of feeding, suggesting an inherent racial predisposition.
Problems with premature infants. Although the nutritional advantages of human milk over cow's milk for full-term and larger premature infants have been demonstrated, serious questions still exist concerning optimal feedings for very small premature infants, especially those with gestational ages of less than 33 weeks.3,1214,27,28,31 It has long been noted that premature infants fed breast milk grow at a slower rate than those fed artificially. In a recent study, Davies12 demonstrated that weight gain, linear growth, and increase in head circumference are impaired in premature infants of 28 to 32 weeks' gestation.
It is likely that the low levels of both protein and mineral content of human milk are responsible for this finding. The long-term sequelae (if any) of this relatively slow rate of growth remain to be determined. There may be, however, a compensating advantage in breast milk of prematurely delivered infants. It contains significantly higher concentrations of nitrogen than does milk obtained from mothers who deliver at term. For a given volume of milk, the premature infant would receive 20 per cent more nitrogen than a term infant.32
Both human milk and currently available artificial formulas present certain nutritional disadvantages for small premature infants. It is hoped that ongoing research in this area will produce a feeding regimen most suited for optimal growth and development of these infants.
Transmission of drug and environmental pollutants. Pharmacologic agents and environmental pollutants are transferred from the maternal circulation to breast milk, with concentrations dependent on the biochemical properties of these substances.15,16
Oral contraceptives may decrease the volume of milk through their estrogenic effect and reduce the concentrations of fat, protein, and calcium. Mothers enrolled in methadone maintenance programs may secrete this substance in their milk in varying concentrations. This is probably a contraindication to breast feeding.
Nicotine, which is probably toxic for the growing fetus during intrauterine life, is present in breast milk of nursing mothers who are cigarette smokers.33 Although specific clinical abnormalities related to nicotine ingestion have not been described in suckling infants of cigarette smokers, a potential danger nonetheless exists for these infants.
Trichlorethylene has been transmitted in breast milk, leading to hepatomegaly and jaundice in an infant. In Bagnell and Ellenberger's report on such transmission,34 the source of this agent was a dry-cleaning solvent.
Theobromine, a major component of chocolate, has also been found in breast milk.35 The effect of this substance on the nursing infant is not known.
DDT is found in higher concentrations in human milk than in cow's milk in areas where it is used.36 Polychlorbiphenyls (PCBs) are industrial contaminants found in heavy concentrations in the waters of Lake Ontario and the upper Hudson River.16 These substances have been detected in milk of lactating women living in these areas. While this poses a potential hazard, no clinical effects of these environmental pollutants on infants have yet been observed. Mercury may be transmitted from mother to infant in breast milk and may cause significant neurologic damage.
Problems when the mother is a vegetarian. A potentially significant problem is the development of a recently described syndrome if the mother is a strict vegetarian. Severe megaloblastic anemia, coma, hypothermia, flaccidity and pigmentation of the extremities, methylmalonic aciduria, hyperglycinemia, and hyperglycinuria were observed.37
Problems with colic if the mother drinks cow's milk. Infantile colic may occur in breast-fed infants if the mother is herself drinking cow's milk. When mothers are put on diets free of cow's milk protein, most of the infants no longer demonstrate colic.38
Infectious agents. Human milk is not sterile, and a number of potentially pathogenic agents may be passed on to the infant. Two significant organisms that have been isolated from human milk are hepatitis-B virus and cytomegalovirus (CMV). Although actual infection of neonates via this route has not been described, the potential problem has been well demonstrated. Rubella virus has also been isolated from breast milk following postpartum maternal immunization.39 Group B streptococcal infection in infants has been associated with isolation of this organism from the breast milk of their mothers. The number of such instances is few, and a true causal relationship is unproved.40,41 This was not associated with clinical disease in the infant.
Failure to thrive. Occasionally, otherwise healthy full-term infants fail to thrive on breast feeding. These infants may be completely asymptomatic or may have excessive crying and irritability. This is due, in many instances, to insufficient feeding and may be reversed by increasing the milk intake.42
The mother who elects to breast-feed her infant must be well motivated and should have the support of her family, obstetrician, pediatrician, and hospital nursing staff. Breast feeding should not be attempted because of outside pressures or guilt feelings.
Colostrum, which has a higher protein but lower caloric content than milk, begins to form during pregnancy, and breast enlargement is noted. It is not until the second to fourth postpartum day that true milk is secreted.
Optimal milk production is predicated upon adequate emptying of the breasts. It is advisable to begin nursing as soon as possible, preferably in the delivery room, in order to enhance lactation, promote mother-infant bonding, and stimulate the production of oxytocic substances, which cause postnatal uterine contractions. Since the infant is usually more active during the first half hour of life than he will be over subsequent hours, this may be another reason for early nursing.
A two-and-a-half to three-hour semidemand feeding schedule during the first days of life is usually satisfactory. Feeding patterns to meet the infant's particular needs are then established. Rooming-in, when available, is usually more conducive to effective breast feeding than care in the traditional newborn nursery.
Both breasts should be offered to the infant for about five minutes at each feeding on the first day. By the third day, one breast should be offered for about 15 minutes, emptying completely. Following this, the second breast should be offered until the infant is satisfied. At the next feeding, the order in which the breasts are offered is reversed.
Good feeding techniques are vital for successful nursing. The infant's lips should be on the areola, and the gums should not clamp down on the nipple. In order to increase nipple protractility prior to nursing, the mother should grasp the areolar margin between her second and third fingers and rotate it. Activation of the rooting reflex is necessary for insuring proper engagement of the nipple in the infant's mouth. When the mouth is gently stroked by the nipple, it turns toward the nipple, facilitating insertion. The nipple should not be forced into the infant's mouth. Once sucking has begun, application of gentle pressure to the areola may enhance milk flow. The infant's nostrils must remain unobstructed during the nursing process. In the vast majority of cases, milk production is adequate to meet all of the infant's nutritional and fluid requirements. Relief bottles should ordinarily not be given until the infant is six to eight weeks old.
In many centers, breast milk is used for feeding very small premature infants who are unable to suck. While freshly expressed milk from the infant's mother is ideal, this is very often impractical. The use of pooled, pasteurized human milk may be an acceptable alternative.
The value of breast-feeding infants has been well established for many years. Its role in decreasing infection and allergy and its nutritional and psychologic advantages are beyond dispute. A major potential problem is the transmission of industrial pollutants to the infant. This phenomenon is being documented with increasing frequency, but only rarely has it been associated with actual illness. The potential for long-term damage, following a latency period of several years, cannot be ruled out.
In spite of the potential hazards of environmental pollutants, it is encouraging to note the increased interest in breast feeding in the United States over the past few years by both the public and medical community. It is to be hoped that this trend will continue not only in this country and other industrial nations but in preindustrial societies as well, where increased use of artificial feedings could be associated with both an elevated birth rate and excessive infant mortality.
1. Hambraeus, L. Proprietary milk versus human breast milk in infant feedings: a critical appraisal from the nutritional point of view. Pediatr. Clin. North Am. 24 (1975), 17.
2. Jelliffe, D. B., and Jelliffe, E. F. P. Human milk, nutrition, and the world resource crises. Science 188 (1975), 557.
3. American Academy of Pediatrics. Standards and Recommendations for Hospital Care of Newborn Infants, Sixth Edition. Evanston, Dl.: American Academy of Pediatrics, 1977.
4. Jackson, R. L. Long term consequences of suboptimal nutritional practices in early life. Pediatr. Clin. North Am. 24 (1977), 63.
5. Hanson, L. A., and Winberg, J. Breast milk and defense against infection in the newborn. Arch. Dis. Child. 47 (1972), 845.
6. Eastham, E. The advantages of breast feeding - the scientific evidence. Pediatr. Dig. Oct. (1977), 15.
7. Barlow, B., et al. An experimental study of acute neonatal enterocolitis: the importance of breast milk. /. Pediatr. Surg. 9 (1974), 587.
8. Hall, B. Changing composition of human milk and early development of an appetite control. Lancet 1 (1975), 779.
9. Jelliffe, E. F. P. Infant feeding practices: associated diseases. Pediatr. Clin. North Am. 24 (1977), 49.
10. Applebaum, R. M. The obstetrician's approach to the breasts and breastfeeding. J. Reprod. Med. 98 (1975), 98.
11. Knodel, J. Breast-feeding and population growth. Science 198 (1977), 1111.
12. Davies, D. P. Adequacy of expressed breast milk for early growth of preterm infants. Arch. Dis. Child. 52 (1977), 296.
13. Fomon, S. J., Ziegler, E. E., and Vazquez, H. D. Human milk and the small premature infant. Am. ]. Dis. Child 131 (1977), 463.
14. Forbes, G. Is human milk the best food for low birth weight babies? Pediatr. Res. 12 (1978), 434.
15. Catz, C. S., and Giacoia, G. Drugs and breast milk. Pediatr. Clin. North Am. 19 (1972), 151.
16. Miller, R. B. PoUutants in breast milk. J. Pediatr. 90 (1977), 510.
17. Gartner, L. M., and Arias, I. M. Studies of prolonged neonatal jaundice in the breast-fed infant. J. Pediatr. 68 (1966), 54.
18. Raiha, N. C. R., et al. Milk protein quantity and quality in low birth weight infants. Pediatrics 57 (1976), 1976.
19. Rassin, D. K., et al. Milk protein quantity and quality in low birth weight infants. IV. Effects on tyrosine and phenylalanine in plasma and urine. J. Pediatr. 91 (1977), 356.
20. Gaull, G. E., et al. Milk protein quantity and quality in low birth weight infants. III. Effects on sulphur amino acids in plasma and urine. J. Pediatr. 90 (1977), 348.
21. Reisser, R., and Sidelman, Z. Control of serum cholesterol homeostasis by cholesterol in the milk of the sucking rat. J. Nutr. 102 (1972), 1009.
22. McMillan, J. A., Landow, S. A., and Oski, F. A. Iron sufficiency in breast-fed infants and the availability of iron from human milk. Pediatrics 58 (1976), 686.
23. Downham, M. A. P. S., et al. Breast-feeding protects against respiratory syncitial virus infections. Br. Med. J. 2 (1976), 274.
24. Larsen, S. A., Jr., and Homer, D. R. Relation of breast versus bottle feeding to hospitalization lor gastroenteritis tn a middle-class U.S. population. J. Paftefr. 92 (1978), 417.
25. Lecce, J. G., King, M. W., and Dorsey, W. E. Rearing regimen producing piglet diarrhea (rotavirus) and its relevance to acute infantile diarrhea. Science 199 (1978), 776.
26. Ford, J. E., et al. Influence of the heat treatment of human milk on some of its protective constituents. J. Pediatr. 90 (1977), 29.
27. Bode, B. H., Vanjonaick, W. J., and Crawford, J. D. Mitigation of cretinism by breast feeding. Pediatrics 62 (1978), 13.
28. Varma, S. K., et al. Thyroid hormone secretions in breast milk. Clin. Res. 26 (1978), 172A.
29. Varma, S. K., et al. Thyroxine, tri-iodothyronine and reverse tri-iodothyronine concentrations in human milk. J. Pediatr. 93 (1978), 803.
30. Fisher, Q., et al. Jaundice and breast-feeding among Alaskan Eskimo newborns. Am. ). Dis. Child. 114 (1976), 859.
31. Feeding the premature infant: more questions than answers. PerinatologylNeonatology 2 (1978), 30.
32. Atkinson, S. A., Bryan, M. H., and Anderson, G. H. Human milk: difference in nitrogen concentration from mothers of term and premature infants. J. Pediatr. 93 (1978), 67.
33. Ferguson, B. B., Wilson, D. J., and Schaffner, W. Determination of nicotine concentrations in human milk. Am. J. Dis. Child. 130 (1976), 837.
34. Bagnell, C, and Ellenberger, H. A. Obstructive jaundice due to a chlorinated hydrocarbon in breast milk. Can. Med. Assoc. J. 117 (1977), 1047.
35. Resman, B. H., Blumenthal, H. P., and Jusko, W. J. Breast milk distribution of theobromine from chocolate. J. Pediatr. 91 (1977), 477.
36. Wilson, D. J., et al. DDT concentrations in human milk. Am. J. Dis. Chad. 125 (1973), 814.
37. Higginbottom, M. C., Sweeturan L., and Nyhan, W. L. A syndrome of methylmalonic aciduria, homocystinuria, megaloblastic anemia and neurologic abnormalities in a vitamin B12 deficient breast-fed infant of a strict vegetarian. N. Engl. J. Med. 299 (1978), 317.
38. Jakobsson, I., and Lindberg, T. Cow's milk as a cause of infantile colic in breast-fed infants. Lancet 2 (1978), 473.
39. Buimovici-Klein, E., et al. Isolation of rubella in milk after postpartum immunization. J. Pediatr. 91 (1977), 939.
40. Kenny, J. F., and Zedd, A. J. Recurrent Group B streptococcal disease in an infant associated with the ingestion of infected mother's milk. J. Pediatr. 91 (1977), 158.
41. Schreiner, R. L., et al. Possible breast milk transmission of Group B streptococcal infection. J. Pediatr. 91 (1977), 159.
42. Evans, T. J., and Davies, D. P. Failure to thrive at the breast an old problem revisited. Arch. Db. Child. 52 (1977), 974.
ADVANTAGES AND DISADVANTAGES OF BREAST FEEDING
COMPOSITION (APPROXIMATE) OF HUMAN MILK, COW'S MILK, AND SEVERAL PROPRIETARY FORMULAS (PER 100 ML.)
IMMUNOLOGIC PROPERTIES OF HUMAN MILK