Vitamin E Bioavailability: Past and Present Insights

Over the past decades several studies have investigated the importance of an adequate vitamin E status to sustain both animal health and production in dairy cows. Cow milk is considered as a remarkable source of bioactive components promoting human health, which has renewed interest in the effects of vitamin E supplementation on its nutritional value, sensory quality and shelf life. Thus, defining relative bioavailability, utilisation and transfer into milk of different vitamin E formulations is particularly important to assess the adequate levels of supplementation for animal health and milk quality. In nature vitamin E is present under one isomeric form, RRR α-tocopherol; when α-tocopherol is synthesized chemically, a racemic mixture of 8 possible isomers of α-tocopherol in equimolar concentrations is produced (all-rac α-tocopherol). The different stereoisomers have different biopotencies in humans and livestock; the conversion factor between RRR and all-rac vitamin E was estimated by early studies on the basis of the rat foetal resorption bioassay, and then extended to other species. Recent advances on the distribution of vitamin E stereoisomers in plasma and tissues have highlighted the need to formulate new conversion factors in dairy cows as well as in humans. On account of this, the present article aims to consider past and recent data related to vitamin E in dairy cow nutrition.