Cholesterol and its precursors in human milk during prolonged exclusive breast-feeding.

Concentrations of cholesterol and its precursors were investigated in human milk from 88 mothers at 2 mo, 28 mothers at 6 mo, and 6 mothers at 9 mo of lactation. These mothers, who were exclusively breast-feeding their infants, collected fore- and hindmilk samples at every feeding over a 24-h period. Samples were analyzed by gas-liquid chromatography and mass spectrometry. Mean (+/- SD) cholesterol concentrations were 0.41 +/- 0.094, 0.46 +/- 0.094, and 0.49 +/- 0.10 mmol/L, respectively. The following cholesterol precursors were identified: squalene, lanosterol, dimethylsterol, delta 8.24-methostenol, lathosterol, and desmosterol. Mean concentrations were 0.04 +/- 0.11, 0.35 +/- 0.13, and 0.29 +/- 0.012 mmol/L for desmosterol, 0.0094 +/- 0.0027, 0.012 +/- 0.0039, and 0.011 +/- 0.0039 mmol/L for squalene, and from 0.0011 to 0.0027 mmol/L for all the other precursors. The precursors' equally low concentrations, except for desmosterol and squalene, and the significant correlations with each other suggest that the mammary gland synthesizes cholesterol from lanosterol by preserving the side-chain double bond and that the rate-limiting step may be the conversion of desmosterol to cholesterol.