Inter- and intra-individual variation in plasma and red blood cell vitamin E after supplementation.

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Abstract
To establish the range of individual blood responses to supplemental vitamin E, 30 healthy subjects ingested 75 mg of deuterium-labelled α-tocopherol with a standard breakfast. Blood was collected at 6, 9, 12, 27 and 51 h post ingestion and deuterated (d6) and non-deuterated (d0) α-tocopherol concentrations were determined in plasma and red blood cells (RBC) by GC-MS. To examine intra-individual responses, 6 of these subjects were re-examined at 6-month intervals over a 30-month period. Post ingestion, the amount of d6-α-tocopherol in blood increased rapidly with time with maximal concentrations seen at 12 h (plasma) and 27 h (RBC) in most subjects. At these times, d6-α-tocopherol concentration ranged from 0.3–12.4 μmol/l in plasma and 0.6–4.09 μmol/l packed cell in RBC. Area under the curve calculations indicated inter-individual differences of α-tocopherol uptake to be 40-fold for plasma (12.9–493.3 μmol h/l) and 6-fold for RBC (24.4–146.1 μmol h/l packed RBC). Intra-individual variation in α-tocopherol uptake was small in comparison and remained relatively constant over the 30-month period. We conclude that vitamin E uptake varies widely in the normal population, although it is comparatively stable for an individual over time. These differences likely arise from variations in the regulation of vitamin E uptake and metabolism between subjects. Factors regulating this process must be better understood before the optimal intake of vitamin E can be ascertained.