immunological properties of human milk may be as important as the nutritional
aspects of human milk. How do we know that human milk really does make a
difference in preventing disease? Many studies show that children who are fed
human milk substitutes end up sick or hospitalized at a much greater rate
than children who breastfeed. For example, diarrhea was significantly reduced
in infants fed human milk compared with bottle-fed and weaned children.9,19,20
Most bacterial infections are caused by organisms that are already colonizing
the host, usually in the gastrointestinal or respiratory tracts. Human milk
may prevent the growth of these bacteria.
several ways in which human milk protects children from infection. Human milk
contains antibodies (immunoglobulins) which can help ward off disease in the
infant. Human milk is particularly high in immunoglobulin A (IgA);10 there
is more IgA in human milk than in serum.6 IgA binds to viruses and
bacteria, particularly those that enter through the gut and other mucus
membranes. This is especially protective of infants, who are always putting
things in their mouths.
to antibodies, human milk also contains lysozyme and lactoferrin, two
antibacterial enzymes which protect against a host of infectious agents,
including E. coli and Staphylococcus.3
also contains whole immune cells called white blood cells. Many of these
cells are phagocytes, so called because they engulf bacteria and viruses,
especially if these germs have IgA attached to them. Other immune cells in
human milk include B cells, which make antibodies, and T cells, which attack
How can these
antibodies and other proteins help the infant if they are swallowed and
digested along with the nutritional components of human milk? It turns out
that these immune factors are resistant to proteolysis in the infant's gut.7,8
Ninety percent of the IgA in human milk exists in a complex with secretory
component (SIgA).10 SIgA is resistant to trypsin digestion in the
human milk protects children from disease is by favoring the growth of
beneficial microorganisms. These benign colonizations prevent dangerous
infections from taking hold. For example, bifidobacteria are more
numerous in breastfed infants than in those fed with human milk substitutes.1,3
This may be because of nucleotide salts present only in human milk, however,
when these nucleotide salts were added to the human milk substitutes, the
growth of bifidobacteria was still discouraged.1
Breastfeeding may also favor the proliferation of bacteria with decreased
virulence.15,21 These strains may be more sensitive to
bactericidal agents in serum, more prone to agglutinization, or less able to
attach to epithelial surfaces.14
does not contain the same proportion of immune cells and antibodies that are
found in the mother's blood, nor does it contain a stationary amount of these
protective agents.4 Human milk contains much more IgA and less
immunoglobulin M than serum does.6 In addition, the type of T
cells predominantly found in human milk is different from the predominant
type of T cell found in serum.17 This is because the mammary
glands themselves contain lymphoid cells which produce the IgA antibodies
needed by the breastfeeding child.10,13,18 This mechanism is
functional throughout lactation. In addition to providing protection from
specific germs in the infant, the production and secretion of these immunological
factors by the mother's mammary gland may be linked to the development of the
child's own immune system.4
said, "yes, human milk benefits infants, but older children cannot
continue to receive immunity by breastfeeding, can they?" The answer to
this question is a resounding yes. Children enjoy health benefits for as long
as they breastfeed. Studies have compared weaned children with breastfeeding
children at 30 months16 and at 36 months,20,23 and
found them to be sicker. In some parts of the world, weaned toddlers have a
mortality rate three and a half times higher than toddlers who receive human
milk.20 Weaning foods and even water from some regions are highly
contaminated with E. coli,2 but even undernourished mothers
from these regions produce ample milk antibodies.5
There are at
least two reasons why breastfeeding continues to benefit older children.
First, human milk contains immune factors regardless of the duration of
lactation. Both lysozyme and SIgA levels have been found in human milk for
the entire period of lactation studied, including the second year.10,12,13
Many of these immune factors would be otherwise unavailable.13 Second,
human milk is more easily tolerated by a sick child than weaning foods. Thus,
breastfeeding ensures that sick children remain hydrated and do not lose
excessive weight. For a more detailed description of how breastfeeding can
help an older child combat a severe illness, see What if he hadn't been nursing?
special cases where human milk is particularly high in immune factors.
Colostrum is exceptionally rich in immune factors, containing more white
blood cells per unit volume than blood.17 Preterm milk also
contains more immune factors than term milk, both in colostrum and mature
milk.11 Newborns and premature infants need immunological
protection more than toddlers, and they get that increased protection in the
human milk they consume. This does not preclude older children from
benefiting immunologically from continuing to breastfeed.
- Balmer SE, Hanvey LS
and BA Wharton. 1994. Arch. Dis. Child Fetal. Neonatal Ed. Mar.
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Becker S, Alim AR and MH Merson. 1982. Trans. R. Soc. Trop. Med. Hyg.
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Klin. Padiatr. Jul;188(4):297-310.
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RM, Fehl LM, Loftin K, Smith EO, Garza C and AS Goldman. 1984. Acta.
Paediatr. Scand. May;73(3):296-301.
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S, Hanson LA, Lidin-Janson G, Lindblad BS and R Sultana 1976. Acta.
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Gothefors L, Ahlstedt S, Hanson LA and J Winberg. 1976. Acta. Paediatr.
- Davidson LA and B Lonnerdal.
1987. Acta. Paediatr. Scand. 76:733-740.
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Freter. 1973. J. Immunol. 111:395.
- Giugliano LG, Meyer
CJ, Arantes LC, Ribeiro ST and R Giugliano. 1993. J. Trop. Pediatr.
- Goldman AS, Garza C,
Nichols BL and RM Goldblum. 1982. J. Pediatr. Apr;100(4):563-7.
- Goldman AS, Garza C,
Nichols B, Johnson CA, Smith EO and RM Goldblum. 1982. J. Pediatr.
- Goldman AS, Goldblum
RM and C Garza. 1983. Acta. Paediatr. Scand. 72:461-462.
- Goldman AS, Goldblum
RM, Garza C, Nichols BL and EO Smith. 1983. Acta. Paediatr. Scand.
- Gothefors L, Olling
S and J Winberg. 1975. Acta. Paediatr. Scand. Nov;64(6):807-812.
- Gothefors L, Olling
S and J Winberg. 1976. Acta. Paediatr. Scand. 64:807.
- Gulick EE. 1986.
Pediatr. Nurs. Jan-Feb;12(1):51-4. The effects of breast-feeding on
- Lindstrand A,
Smedman L, Gunnlaugsson G and M Troye-Blomberg. 1997. Acta. Paediatr.
- Lodinova R and V
Jouja. 1977. Acta. Paediatr. Scand. Nov;66(6):705-708.
- Mahalanabis D, Alam
AN, Rahman N and A Hasnat. 1991. Int. J. Epidemiol. Dec;20(4):1064-1072.
- Molbak K, Gottschau
A, Aaby P, Hojlyng N, Ingholt L and AP da Silva. 1994. BMJ. May
- Orskov F and KB
Sorenson. 1975. Acta. Pathol. Microbiol. Scand. [B] Feb;83(1):25-30.
- Parkin DM,
MacClouland DBL, Samson RR, McA Less, M and DJC Shearman. 1973. Europ. J
Clin Invest. 3:66.
- van den Bogaard C,
van den Hoogen HJ, Huygen FJ and C van Weel. 1991. Fam. Med.