A main drawback of vitamin E is the general lack of benefit of supplementation on health outcomes (except in people with vitamin E deficiency). Another main drawback is that high-dose vitamin E can have adverse effects — while the normal dietary intake of vitamin E is safe and necessary, “more is not always better”.[1][2][3][4]
For example, meta-analyses indicate that the long-term intake of high levels of vitamin E — greater than 300–400 IU/day or 135–180 mg/day — might slightly increase all-cause mortality[5][6][7][8][9] and the risk of certain cancers, like prostate cancer and bladder cancer.[10][11][12] In patients with heart disease or type 2 diabetes, long-term high-dose vitamin E supplementation has also been linked to a small increase in heart failure risk.[13] Furthermore, in some studies, participants who took very high doses have reported nausea, diarrhea, fatigue, or blurred vision.
High levels of vitamin E intake can worsen the impairment in blood clotting found in people with vitamin K deficiency,[2] leading to a higher tendency of bleeding.[14] For example, one meta-analysis found that supplementation with vitamin E was associated with a 22% higher risk of hemorrhagic stroke (a severe form of stroke associated with bleeding in the brain).[15]
The recommended dietary allowance (RDA) for vitamin E in adults is 15 milligrams per day, and the tolerable upper intake level (UL) for vitamin E in adults is 1,000 milligrams per day.[4] The adverse effects described above are typically associated with long-term daily intakes greater than the RDA. Given the risks, the lack of benefits, and the ease with which vitamin E can be obtained in the diet, supplementation with vitamin E is rarely necessary. Seek advice from your doctor if you are unsure.