woman is low and iodine deficiency is evident in approximately 75% of the population (Delange, 1985).

CONSTITUENTS OF HUMAN MILK WITH OTHER BIOLOGIC FUNCTIONS

Very few studies have been conducted to investigate the effects of maternal nutrition on the composition of nonnutritive substances in human milk. Research in this area is warranted, however, because of the important biologic functions of many of these substances. Briefly, these constituents have the following functions.

  • nutrient synthesis, assembly, and utilization;

  • direct protection against microbial pathogens;

  • modulation of inflammatory processes;

  • promotion of growth and maturation of selected systems by supplying inducers, such as growth factors and hormones;

  • enhancement of neural transmission;

  • catalysis (increasing the rate) of some metabolic reactions (Hamosh and Hamosh, 1988; Koldovský, 1989).

The many complex functions of milk constituents can be illustrated by describing the role of the milk protein α-lactalbumin, which constitutes approximately 25 to 30% of the total protein in human milk and thus is a major supplier of amino acids to the developing infant. It also is one of the two protein components of the system that synthesizes lactose within the mammary gland. In addition, α-lactalbumin is a metalloenzyme with calcium- and zinc-binding sites and is structurally similar to lysozyme (an antibacterial enzyme discussed below) (Hall and Campbell, 1986). Other examples of nonnutritive functions of milk proteins are given below and in Table 6-3.

TABLE 6-3 Examples of the Multiple Functions of Proteins in Human Milka

 

Proteins

Function

α-Lactalbumin

Lactoferrin

Secretory IgA

BSS Lipase

EGF

Synthesis of a nutrient

x

o

o

x

o

Carrying metals

x

x

o

o

o

Preventing infection

?

x

x

o

o

Preventing inflammation

?

x

x

o

x

Promoting growth

o

x

o

o

x

Catalyzing reactions

o

o

o

x

x

a Abbreviations: IgA = immunoglobulin A; BSS = bile salt stimulated; EGF = epidermal growth factor. x indicates that the protein exhibits this function; o indicates that it does not.



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