Abstract
Vitamin E (α-tocopherol) is recognised as a key essential lipophilic antioxidant in humans protecting lipoproteins, PUFA, cellular and intra-cellular membranes from damage. The aim of this review was to evaluate the relevant published data about vitamin E requirements in relation to dietary PUFA intake. Evidence in animals and humans indicates a minimal basal requirement of 4-5 mg/d of RRR-α-tocopherol when the diet is very low in PUFA. The vitamin E requirement will increase with an increase in PUFA consumption and with the degree of unsaturation of the PUFA in the diet. The vitamin E requirement related to dietary linoleic acid, which is globally the major dietary PUFA in humans, was calculated to be 0·4-0·6 mg of RRR-α-tocopherol/g of linoleic acid. Animal studies show that for fatty acids with a higher degree of unsaturation, the vitamin E requirement increases almost linearly with the degree of unsaturation of the PUFA in the relative ratios of 0·3, 2, 3, 4, 5 and 6 for mono-, di-, tri-, tetra-, penta- and hexaenoic fatty acids, respectively. Assuming a typical intake of dietary PUFA, a vitamin E requirement ranging from 12 to 20 mg of RRR-α-tocopherol/d can be calculated. A number of guidelines recommend to increase PUFA intake as they have well-established health benefits. It will be prudent to assure an adequate vitamin E intake to match the increased PUFA intake, especially as vitamin E intake is already below recommendations in many populations worldwide.
Highlights
Molecular structure and function of vitamin EVitamin E has eight isoforms; it can be categorised into tocopherol isoforms, which have a saturated side chain on the chromanol ring, and into tocotrienol isoforms, which have an unsaturated side chain
PUFA, categorised into n-3 and n-6 fatty acids, are important cell membrane components and key elements in child development, brain and visual functioning and physical health and well-being throughout the life course
As current vitamin E intakes are below the recommended intakes in more than 90 % of North Americans as well as in some European Countries[5], and at the same time people are being encouraged to increase their intake of PUFA, especially those with high degree of unsaturation, because of their reported health benefits, the ratio of vitamin E:PUFA in the human diet appears to become more critical and requires a deeper examination
Summary
Vitamin E has eight isoforms; it can be categorised into tocopherol isoforms, which have a saturated side chain on the chromanol ring, and into tocotrienol isoforms, which have an unsaturated side chain. Other factors play a key role in determining whether a molecule has in vivo bioactivity; RRR-α-tocopherol has the highest in vivo bioactivity of all vitamin E isomers It is bound by a specific transport protein – the α-tocopherol transfer protein (α-TTP). Vitamin E is the key essential lipophilic (fat-soluble) antioxidant located in human cell membranes protecting them from oxidative damage. A recent study in pregnant women observed that the rate of miscarriages was significantly increased in women having a low concentration of α-tocopherol (20 μmol/l with an optimum plasma level of about 30 μmol/l(36–39)
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