You are missing the point. Above a certain level, the negative side effects start out weighing the positive affects. So just because something is not close to toxicity, does not mean it is actually having a net benefit on your health. With vitamins, take the recommended dosage, or preferably slightly less, as it is likely you are getting at least something from your diet, not matter how poor. Anything above that is likely to start having negative effects that start to outweigh any benefits. Most adults get sufficient vitamins and minerals from their diet, even a poor western diet. Vitamin D however, is the exception if you don't get enough sun.
I'm not talking about vitamins in general; I'm talking about vitamin D and how embarrassingly low the U.S. RDA is.
There are a great many Americans who would see immense benefit by taking (say) 1,000 to 2,000 IU of vitamin D per day. And I feel pretty confident there are no people for whom an extra 2,000 IU would be negative.
