Clinical trials have suggested an increase in all-cause mortality with high dose (greater than 400 international units/day) vitamin E supplements. Large doses of vitamin E can also increase the vitamin K requirement and can result in bleeding in patients taking oral anticoagulants.
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et al. The effectiveness of vitamin E treatment in Alzheimer's disease. Int J Mol Sci. 2019 Feb 18;20(4).
et al. Vitamin E supplementation in people with cystic fibrosis. Cochrane Database Syst Rev. 2017 Mar 6;3:CD009422.