Vitamin E is a fat soluble vitamin naturally present in vegetable oils and in other fatty foods. Previously, the term vitamin E was used as the generic term for four tocopherols (α, β, γ, δ) and four tocotrienols (α, β, γ, δ), that are organic compounds which possess antioxidant activity to a different degree. Now only α- tocopherol is considered as vitamin E. Its natural or synthetic form with the highest bioavailability is RRR-α-tocopherol. Commercially available forms normally include either the natural and the other stereoisomers (8 in total) and are called all-rac-α-tocopherol, or their esterified forms as acetate or succinate. The biological activity expressed as International Unit (UI) of RRR-α-tocopherol and all-rac-α-tocopherol is respectively 1.49/1. Efficient α-tocopherol absorption requires the presence of fat. After its intestinal absorption, α-tocopherol is incorporated into chylomicrons, and transported to the liver. There, the specific α-tocopherol transfer protein (α-TTP), is responsible for its incorporation into nascent very low-density lipoproteins (VLDL) to be secreted by the liver into the circulation and distributed to body tissues.
Biochemical functions and deficiency of vitamin E
Alpha-tocopherol mainly functions as a lipid-soluble antioxidant that prevents propagation of free-radical reactions. The vitamin is a peroxyl radical scavenger and especially protects PUFAs within membrane phospholipids and plasma lipoproteins (Wang and Quinn, 1999; Traber and Atkinson, 2007; Niki, 2014). When peroxyl radicals are formed, these react 1 000-times faster with α-tocopherol than with PUFAs (Buettner, 1993). By protecting PUFAs within membrane phospholipids, α-tocopherol preserves intracellular and cellular membrane integrity and stability, plays an important role in the stability of erythrocytes and the conductivity in central and peripheral nerves, and prevents haemolytic anaemia and neurological symptoms (ataxia, peripheral neuropathy, myopathy, pigmented retinopathy) occurring in α-tocopherol-deficient individuals (Muller, 1986).
The classification of ‘vitamin E’ as an essential nutrient is based on animal studies and primary and secondary α-tocopherol deficiency in humans. The need for α-tocopherol in order to prevent fetal resorption in pregnant rats is at the origin of the discovery of the vitamin (Evans and Bishop, 1922). The chemical name ‘tocopherol’ derives from its essentiality for normal reproduction in animals, though the essentiality for this function has never been demonstrated in humans (Brigelius-Flohe et al., 2002). Primary α-tocopherol deficiency is familial isolated. Secondary α-tocopherol deficiency has been observed in cases of abetalipoproteinaemia, cholestatic liver diseases, severe malnutrition, fat malabsorption, and cystic fibrosis (Farrell et al., 1977; Jeffrey et al., 1987; Eggermont, 2006; Zamel et al., 2008).
Symptomatic α-tocopherol deficiency in individuals without any disease and who consume diets ‘low’ in α-tocopherol has not been reported (IOM, 2000). Mean Nutrient Reference Values (NRV) of alpha-tocopherol with a normal diet for Italian population are 12 mg/die.
(EFSA 2015, mod.)
E-Plus is a food supplement with vitamin C developed by Volchem.
More articles:
RELATED PRODUCTS