-α-Tocopherol Is the Predominant Stereoisomer of α-Tocopherol in Human Milk.

Background: The naturally occurring α-tocopherol (α-T) stereoisomer, -α-tocopherol (-α-T), is known to be more bioactive than -α-tocopherol (-α-T), a synthetic racemic mixture of 8 stereoisomers. There is widespread use of -α-T in maternal supplements.

Objective: The aim of the study was to thoroughly describe the α-T stereoisomer profile of human milk.

Methods: We measured the α-T stereoisomer profile in milk from 2 cohorts of women: a cohort of 121 women who provided milk on days 30 and 60 of lactation (study 1) and a separate cohort of 51 women who provided milk on days 10, 21, 71, and 120 of lactation (study 2).

Results: -α-T was the predominant stereoisomer ( < 0.0001) in all samples in both studies despite a large intrasubject range in total α-T (0.7-22 μg/mL). On average, -α-T comprised 73-76% of total α-T, but average values for the synthetic stereoisomers were , 8-14%; , 6-8%; , 5-6%; and the sum of stereoisomers (Σ), 3-5%. Despite the predominance of -α-T, the sum of the synthetic stereoisomers comprised as much as 48% of total α-T. We calculated the ratio of to the sum of the synthetic ( +  + ) stereoisomers (s) to assess the degree to which is favored in milk Consistent with discrimination among 2 stereoisomers in mammary tissue, /s2 values ranged from 2.8 to 3.6, as opposed to the expected ratio of 0.33 if there was no discrimination. However, the to s ratio did not correlate with milk α-T concentration, but both components of the ratio did.

Conclusions: -α-T is the predominant stereoisomer in human milk, concentrations of synthetic 2 stereoisomers were notable, and the relation between milk total α-T and stereoisomer profile is complex. Due to the wide range found in milk α-T stereoisomer profile, investigation into its impact on α-T status and functional outcomes in breastfed infants is warranted.