Iron in human milk.

The distribution of iron among various fractions of human milk was determined by gel filtration, ultrafiltration, and atomic absorption spectrophotometry. Total iron varied between 0.26 and 0.73 microgram/ml; 1.5 to 46% of the iron was bound to the lipid fraction and 18 to 56% was found in a low molecular weight fraction. Only a small amount of iron was bound to lactoferrin, the major iron-binding protein of human milk; the iron saturation of this protein was found to be 1 to 4%, at the most. Thus, much less iron is bound to lactoferrin than earlier reported; this may be important in regard to the suggested role of this protein as a bacteriostatic agent. A correlation was found between iron and fat content during the course of a single nursing, but not between iron and lactoferrin.