Fatty Acid Profile Comparisons in Human Milk Sampled From the Same Mothers at the Sixth Week and the Sixth Month of Lactation

Objectives: To compare fatty acid composition of human milk at 2 different stages of lactation and investigate the relation between trans isomeric and long-chain polyunsaturated fatty acids (LCPUFAs) in human milk at the sixth month of lactation. Subjects and Methods: We investigated human milk samples obtained at the sixth week and sixth month of lactation from 462 mothers who participated in a large birth cohort study. Fatty acid composition of human milk lipids was determined by high-resolution capillary gas-liquid chromatography. Results: Fat contents of human milk increased significantly between the sixth week and sixth month of lactation (1.63 [2.06] and 3.19 [3.14], g/100 mL; median [interquartile range], P< 0.001). Percentage contributions to human milk fatty acid composition of nearly all polyunsaturated fatty acids also increased significantly (linoleic acid: 10.09 [4.41] and 11.01 [4.53], arachidonic acid: 0.46 [0.32] and 0.48 [0.23], a-linolenic acid: 0.69 [0.42] and 0.75 [0.41], and docosahexaenoic acid: 0.17 [0.23] and 0.23 [0.15], % wt/wt, P< 0.001). Values of the 18-carbon trans octadecenoic acid (C18: 1n-7/9t) significantly inversely correlated to linoleic acid (r = -0.24, P< 0.001), a-linolenic acid (r = -0.19, P< 0.001), and arachidonic acid (r =-0.43, P< 0.001). In contrast, we found no correlation between the 16-carbon trans hexadecenoic acid (C16: 1n-7t) and the same LCPUFAs. Conclusions: Data obtained in the present study indicate increasing fat contents with stable or increasing percentage contribution of LCPUFAs in human milk samples between the sixth week and at the sixth month of lactation, and the availability of 18-carbon trans isomeric fatty acids is inversely associated to the availability of several LCPUFAs in human milk at the sixth month of lactation.