Vitamin E
(α-tocopherol)
Vitamin E (α-tocopherol) neutralises free radicals and protects tissues and organs from oxidative damage. It is incorporated into cell membranes, modulates expression of various genes, has a role in neurological function, cell signalling, inhibits platelet aggregation, enhances vasodilation and can modulate the immune response. Date of preparation: January 2019
Contribution:
Importance of vitamin E for health
Vitamin E is a fat-soluble antioxidant vitamin that exists in eight natural chemical forms with varying levels of biological activity. All forms are absorbed but α-tocopherol is the major biological form and is preferentially retained in the body through binding with α-tocopherol-transfer protein (α-TTP) and as such is the only recognised form to meet human requirements. There are 7 other forms existing in nature: β-, γ-, δ-tocopherol, and α-, ß-, γ-, and δ-tocotrienol (1).
The liver takes up vitamin E ingested in the diet, and re-secretes preferentially only α-tocopherol; other forms of vitamin E are excreted (2). Serum concentrations of α-tocopherol therefore depend on the action of the liver, and the hepatic α-tocopherol transfer protein (α-TTP) is considered as the major regulator of vitamin E status in humans (3).
Vitamin E function
α-tocopherol neutralises free radicals and protects tissues and organs from oxidative damage. It is incorporated into cell membranes, prevents protein oxidation and lipid peroxidation, and therefore maintains the membrane integrity. α-tocopherol also modulates expression of various genes, has a role in neurological function, cell signalling, inhibits platelet aggregation, enhances vasodilation and can modulate the immune response by reducing the proliferation of immune cells (1, 4).
Vitamin E for health conditions
There has been considerable researchconducted about the benefits of vitamin E on certain medical conditions, due to its role as a potent antioxidant. Conditions include cardiovascular disease, cancer, age-related macular degeneration and Alzheimer’s disease. To date, results are inconclusive and there are no recommendations in place. This is partially due to the lack of validated biomarkers of vitamin E linking intake to clinical outcomes (5), making this a research priority area.
Vitamin E supplemementation to prevent morbidity and morality of preterm infants
Premature infants are born before 37 weeks of gestation. Premature births are the leading cause of infant death in the first 4 weeks of life. Incidence of prematurity is increasing; prevalence is currently 1 in 10 births globally. Risks of mortality due to prematurity are highest in low-income settings (6).
Vitamin E is important for the health of premature infants, and may be able to prevent or limit morbidity associated with prematurity. Vitamin E is present at higher than usual levels in the breast milk of mothers who have given birth prematurely. However, though studies have shown some benefits of vitamin E supplementation to premature infants, supplem
entation with vitamin E may also increase the risk of life-threatening infections e.g. sepsis.
Current evidence does not support the use of high-dose vitamin E supplementation, and WHO state that further research is needed before specific recommendations can be made.
Sources of vitamin E
Vitamin E is naturally abundant in the diet, with the principal sources being vegetable oils, particularly sunflower and safflower, nuts, seeds and green leafy vegetables such as spinach (3). Vitamin E in either natural or synthetic form, as α-tocopherol, is also commonly consumed as a dietary supplement (4), or in fortified ready-to-eat cereals (3).
Fortified cooking oils are used in many low- and middle-income settings, and the World Food Programme (WFP) currently recommends the addition of Vitamin A and Vitamin D as fortificants of vegetable oils, though vitamin E is currently not included in the recommendations. (For more information, see these pages from the WFP.) However, the stable form, α-tocopherol acetate form may be added to oils, and is converted to α-tocopherol in the intestine. Due to its stability it is a good food fortificant, however it offers the oil no antioxidant protection. (For more information, see this factsheet from DSM.)
Deficiency
A deficiency in vitamin E is rare, and most people with a healthy, balanced diet will obtain enough vitamin E from dietary sources (5). However, those with low-fat or severely fat-restricted diets may be at risk of insufficient intakes (5), because fat is required for vitamin E absorption. Persons at risk of frank vitamin E deficiency are those with genetic abnormalities in the α-TTP transfer protein in the liver, those with genetic abnormalities in lipoprotein synthesis, or those with fat malabsorption syndromes (3)Symptoms of vitamin E deficiency include peripheral neuropathy, ataxia, skeletal myopathy, retinopathy, and impairment of the immune response (5).
Excess
There are no documented effects of an excessive consumption of vitamin E from food sources (5). The excessive consumption of vitamin E from supplements appears to be of minimal risk however there may be a risk of haemorrhage. The precise effects are unclear and warrant further investigation (5).