Long-chain polyunsaturated fatty acid concentrations in human hindmilk are constant throughout twelve months of lactation.

We assessed the total fat content and fatty acid concentrations in colostrum and throughout a nursing period of 12 months in a group of mothers recruited after delivery of full-term infants. Pooled human milk (hindmilk) was collected from all feedings over 24 hours at the following times: 1st day of nursing (colostrum), and at 1, 3, 6, 9, and 12 months. Total fat was quantified by a microgravimetric method. Fatty acids were analyzed by means of capillary gas chromatography. Comparisons were made with analysis of variance for repeated measures. Ten mothers completed the follow-up 12-month nursing period. We found that the total lipid content of hindmilk (mg/dL) rises more than 3-fold from the colostrum up to the 3rd month, and then more slowly up to the 12th month. Total saturated fatty acids progressively increase and total monounsaturated FA progressively decrease. Among long-chain polyunsaturated fatty acids, we found that the concentrations (mg/dL) of C20:4 and C22:6 remain stable from colostrum up to the 12th month of nursing, while their percentage levels are highest in colostrum and decrease afterwards in association with the increase in total fats. The C18:2n6 and C18:3n3 amounts progressively increase, following the trend of total fats. These data indicate that the secretion of arachidonic acid and docosahexaenoic acid during lactation remains constant, in spite of changes in total fat and in the linoleic acid and alpha-linolenic acid contents of milk.