Vitamin E in human health and disease.
Vitamin E in nature is comprised of a family of tocopherols and tocotrienols. The most studied of these is alpha-tocopherol (alpha-TOH), because this form is retained within the body, and vitamin E deficiency is corrected with this supplement. alpha-TOH is a lipid-soluble antioxidant required for the preservation of cell membranes, and it potentially acts as a defense against oxidative stress. Many studies have investigated the metabolism, transport, and efficacy alpha-TOH in the prevention of sequelae associated with cardiovascular disease (CVD). Supplementation with vitamin E is considered to provide health benefits against CVD through its antioxidant activity, the prevention of lipoprotein oxidation, and the inhibition of platelet aggregation. However, the results from large prospective, randomized, placebo-controlled clinical trials with alpha-TOH have been largely negative. A recent meta-analysis suggests that alpha-TOH supplements may actually increase all-cause mortality; however, the mechanism for this increased risk is unknown. In vitro studies performed in human cell cultures and animal models suggest that vitamin E might increase the hepatic production of cytochrome P450s and MDR1. Induction of CYP3A4 or MDR1 by vitamin E could potentially lower the efficacy of any drug metabolized by CYP3A4 or MDR1. Other possibilities include an adverse effect of alpha-TOH on blood pressure in high-risk populations. Because of the wide popularity and use of vitamin E supplements, further research into potential adverse effects is clearly warranted.
Clarke
Michael W
MW
School of Medicine and Pharmacology, University of Western Australia, Crawley, WA, Australia.
Burnett
John R
JR
Croft
Kevin D
KD
D000818:Animals; D000975:Antioxidants / Q000502:physiology*; D002318:Cardiovascular Diseases / Q000517:prevention & control; D051544:Cytochrome P-450 CYP3A / Q000096:biosynthesis; D004790:Enzyme Induction; D006801:Humans; D008074:Lipoproteins / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010919:Placebos; D016032:Randomized Controlled Trials as Topic; D014810:Vitamin E / Q000502:physiology*
D000975:Antioxidants; D008074:Lipoproteins; D010919:Placebos; D014810:Vitamin E; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human