Abstract: In this study, the composition and content of vitamin D and its esters in 108 human milk samples from different lactation stages (colostrum on days 0–7, transition milk on days 8–15 , and mature milk after day 16) were analyzed by ultra-high performance liquid chromatography/quadrupole time of flight mass spectrometry (UPLC/Q-TOF-MS). The results showed that human milk contained 4 kinds of vitamin D and 20 kinds of vitamin D esters, 16, 18 and 14 kinds of vitamin D esters being found in colostrum, transition milk and mature milk, respectively. During the whole lactation period, the average contents of vitamin D2 and 25(OH)-D3 in colostrum were highest, 26.83 and 160.67 ng/L, respectively; the average content of vitamin D3 in transition milk was highest, 119.87 ng/L; and the average content of 1,25(OH)2-D3 in mature milk was highest, 1.82 ng/L. The average contents of vitamin D esters in colostrum, transition milk and mature milk were 11.89, 10.73 and 11.47 ng/L, respectively, and the content of vitamin D2 tetradecenoate (C14:1) was highest throughout the lactation period. Through partial least squares-discriminant analysis (PLS-DA), colostrum, transition milk and mature milk could be well separated, indicating that the types and contents of vitamin D and vitamin D esters in human milk change from colostrum to mature milk. There was a correlation between different vitamin D esters. This study could provide data support for the development of infant formula.

Key words: human milk; vitamin D; vitamin D esters; qualitative analysis; quantitative analysis