Actually, it needs to be mentioned that NOBODY can answer how much is enough.
Nobody here knows your current health, other vitamin intake, metabolism, food intake, environment pollution levels, the medications or herbs you take, your immune system condition, nor your underwear size and how much hair you have on your back.
-Ok, the last 2 are irrelevant but ALL THE OTHERS ARE NOT.
We cannot tell you how much to take. We can only state what is a relevant "safe" "average" dosage is. You need to take other factors as I have just listed into account and decide for yourself unless you have someone take all your variables and plan out a complete nutritional and exercise plan.
The body doesn't know how much a milligram is or how much a capsule is. It only knows it uses what you give it, and sometimes it needs more or less.
Personally, I find most adults can easily handle more than 500, but it would be incredibly bad of me to try to reccommend any dosage level without knowing what I am applying that to.