While it is possible that a higher dose of vitamin E than that tested in Physicians' Health Study II1 (400 IU of synthetic vitamin E every other day) may be required to reduce the incidence of age-related cataract, the dose tested1 exceeded doses associated with lower risks of cataract in observational studies. Similar null results for cataract were observed in the Women's Health Study,2 which tested natural-source vitamin E (600 IU every other day).
Christen WG. Vitamin E and Age-Related Cataracts—Reply. Arch Ophthalmol. 2011;129(6):805-820. doi:10.1001/archophthalmol.2011.107