Why are you only taking Vitamin D if you believe "an ounce of prevention's worth a pound of cure"? Shouldn't you be taking a multi-vitamin, at least, in order to hit all the other vitamins & minerals you might be short on?
Good point - during my annual exams I find that I'm usually within good levels on all other nutrients that I get tested on, but I guess I'll find out in a few weeks when my next one comes around. Every multi-vitamin is different and I'm concerned about going over the limit on other nutrients like Potassium or something of the sort(a long time ago, I found myself too high on that particular one, and I wasn't on any supplements). I simply haven't had a chance to research each one in detail.