No more than 300iu!
Anything more than 300iu of vitamin e
is overkill, and larger doses have been shown to be associated with higher mortality.
Speculation, is that while essentil, it is a relatively week anti-oxidant, compared to tea, colored fruits and veggies, and too much will block out their more potent effects. Vitamin e is more than an anti-oxidant and has other functions. They should be met at 100iu or less!