Background
Recent studies indicated that non-cholesterol sterols such as plant sterols and intermediates of endogenous cholesterol synthesis modulate the immune system in certain diseased conditions, such as allergic asthma. Breast milk is relatively high in non-cholesterol sterols, and regulated transport of these compounds to breast milk suggests an important role in infant health. Therefore, the aim of this study is to explore associations between non-cholesterol sterol concentrations in breast milk and allergic outcomes in the first two life years.

Methods
Data from the KOALA Birth Cohort Study, the Netherlands were used. Eight sterols were analyzed by gas-liquid chromatography–mass spectrometry in breast milk that was sampled one month postpartum (N=311). Sterols of interest were selected using exploratory factor analysis and independent sample t-tests for allergic outcomes eczema, wheeze, and allergic sensitization. Associations between sterols with allergic outcomes were analyzed using multiple logistic regression to calculate odds ratios (ORs).

Results
The odds of eczema in the first two life years were lower with higher concentrations of cholestanol (OR (95%CI): 0.98 (0.95; 1.00), p=0.04), lanosterol (0.97 (0.95; 1.00), p=0.02), lathosterol (0.93 (0.87; 0.99), p=0.02), and stigmasterol (0.51 (0.29; 0.91), p=0.02) in breast milk one month postpartum. Furthermore, odds of allergic sensitization at age 2 were lower with a higher concentration of campesterol in breast milk (OR (95%CI): 0.82 (0.70; 0.94), p=0.01). None of the sterols were associated with wheeze in the first two life years.

Discussion
Higher concentrations of several sterols in breast milk were associated with reduced risk of having eczema and allergic sensitization in the first two life years. These results support our hypothesis that non-cholesterol sterols in breast milk may influence the maturation of the immune system of infants and thereby potentially preventing allergic outcomes. However, the results need replication because of the study’s exploratory nature.