A critical review of methodologies used in determination of relative bio‐availability ratio of RRR ‐α‐tocopheryl acetate and all ‐ rac ‐α‐tocopheryl acetate

Bio‐availability of different α‐tocopherol forms in livestock animals is measured by the increase in plasma or tissue concentrations of α‐tocopherol after oral administration. It is generally accepted that RRR ‐α‐tocopheryl acetate (natural source vitamin E derived from vegetable oil) has a higher bio‐availability compared to all ‐ rac ‐α‐tocopheryl acetate (synthetic vitamin E, i.e. α‐tocopherol produced by chemical synthesis). However, different bio‐availability ratios have been reported in the literature. The major reason for conflicting results in literature studies was the inability to separate the proportion of α‐tocopherol originating from test materials, from the proportion of α‐tocopherol originating from basal dietary ingredients and pre‐feeding. This causes significant variability. For bio‐availability determination, a baseline or control treatment is essential. The estimation of bio‐availability without correction for basal vitamin E status will lead to incorrect interpretation of the results. When using proper methodologies, it is possible to correct for the impact of α‐tocopherol intake from basal ingredients and α‐tocopherol originating from pre‐feeding, therefore yielding results reflecting the true relative bio‐availability of different α‐tocopherol substances. When reviewing literature data a critical evaluation of the method used in determination of relative bio‐availability is recommended. Copyright © 2010 Society of Chemical Industry