Vitamin E refers to eight compounds (vitamers: tocopherols and tocotrienols) and is found in both plants and animal foods (1). The most studied natural source of vitamin E is alpha-tocopherol because of its prevention of lipoprotein oxidation and inhibition of platelet aggregation, which suggests prevention of cardiovascular disease (1).
Alpha-tocopherol is the only one with biological activity and offers the most protection against oxidative stress through its oxygen-quenching capacity (2). The natural and most active form is designated by its steroisomer RRR alpha-tocopherol and continues to be found on supplement labels as d-alpha tocopherol (2).
Beta-tocopherol also exhibits oxygen-quenching capacity albeit not as much as alpha-tocopherol and its abilities are followed by gamma- and delta-tocopherol (2). The tocotrienols may not exhibit significant antioxidant role, but have another role in which they reduce plasma cholesterol concentration (2).
A recently discovered natural form of vitamin E is alpha-tocopheryl phosphate found to be ubiquitous in tissues of animals and plants (3). Its role is not yet clear.
Supplementation with vitamin E is widely popular for taking guesswork out of how to get enough of this seemingly non-toxic vitamin for cardiovascular health (1;4). Newer research on vitamin E, however, is showing that it may be possible that people are taking too much (1;5).
Clinical trials on alpha-tocopherol have mostly found negative results including possible increased adverse effects on those with high blood pressure and increased risk of death in those with cardiovascular disease (1).
Until further is known about the most appropriate amount to take for reduced risk of disease, the Recommended Dietary Allowance for vitamin E continues to be 15 mg daily, based on the natural form of alpha-tocopherol, and is still considered one of the least toxic vitamins (2).
Reference List
1. Clarke MW, Burnett JR, Croft KD. Vitamin E in human health and disease. Crit Rev Clin Lab Sci 2008;45:417-50.
2. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.
3. Gianello R, Libinaki R, Azzi A et al. Alpha-tocopheryl phosphate: a novel, natural form of vitamin E. Free Radic Biol Med 2005;39:970-6.
4. Gutierrez AD, de Serna DG, Robinson I, Schade DS. The response of gamma vitamin E to varying dosages of alpha vitamin E plus vitamin C. Metabolism 2009;58:469-78.
5. Bell SJ, Grochoski GT. How safe is vitamin E supplementation? Crit Rev Food Sci Nutr 2008;48:760-74.
