Changes in specific nutrients in breast milk during extended lactation.

An increasing trend towards breast-feeding infants beyond 6 mo of age has been observed in this country. The present study was designed to examine the effect of extended lactation on the concentrations of vitamins B6 and C, free and total folacin, calcium, zinc, and magnesium. Forty mothers were studied from 7 months of lactation until they stopped breast-feeding. Subjects were requested to collect milk samples monthly at a morning feeding between 7 AM and 10 AM. Between 7 and 25 mo of lactation, levels of zinc, calcium, vitamin B6, and vitamin C tended to decrease, whereas levels of free and total folacin remained unchanged. Magnesium levels decreased only after 18 mo of lactation. The decrease in concentrations of zinc and calcium paralleled the decrease in feeding frequency. Changes observed in this study on the composition of human milk may reflect physiological changes in the mammary gland during weaning.