RESUMEN
The vitamin A and beta-carotene contents of breast milk were determined at different stages of lactation in three population groups: nonprivileged Ethiopian, privileged Ethiopian, and Swedish mothers. In addition, a fractionation of vitamin A giving the proportion of retinol was performed. The concentrations of retinol-binding protein (RBP) and (in part of the material) beta-carotene and prealbumin in plasma were also measured. The mean concentrations of vitamin A and beta-carotene in the milk from the Swedish mothers (period 0.5 to 6.5 months) were in the range of 40.0 to 53.1 and 16.3 to 20.8 mug/100 ml, respectively. For the privileged Ethiopian mothers (period 0.5 to 3.5 months) the corresponding ranges were 36.2 to 36.4 and 26.2 to 28.1 mug/100 ml and for the nonprivileged Ethiopian mothers (period 0.5 to 6.5 months) 28.1 to 33.1 and 23.9 to 25.6 mug/100 ml. Only the nonprivileged Ethiopian mothers were examined during a later stage of lactation (6.5 to 11.5 and 11.5 to 23.5 months). The concentrations of vitamin A and beta-carotene in their milk showed a downward trend. The proportion of retinyl ester (percentage of total vitamin A content) was significantly higher in the milk of Swedish mothers than in privileged and nonprivileged Ethiopian mothers. In the Swedish mothers retinol constituted 3.5% of the total vitamin A content of the milk; in Ethiopian mothers it was 15 to 30%. Determination of RBP in plasma showed normal values for Swedish mothers and lowered values for Ethiopian mothers--particularly the nonprivileged, in whom 14 of 81 values were below 20 mug/ml. RBP was demonstrated in colostrum, but only in a low concentration (in the order of 5 mug/ml).