Joanne started with a 25-hydroxy vitamin D level of 23 ng/ml--severe deficiency.
What made this starting value even worse was that it was drawn in August after a moderately sunny summer spent outdoors. (Last summer, not this summer.) It therefore represented her high for the year, since vitamin D levels trend lower as fall and winter set in. This suggests that her winter level was likely in the teens or even single digits. In addition, note that, at age 43, Joanne has lost much of her ability to activate vitamin D in the skin.
So I advised that she take 6000 units of an oil-based gelcap per day, a dose likely to generate the desired blood level, which I believe is 60-70 ng/ml.
Four months later, her 25-hydroxy vitamin D level: 39.9 ng/ml--still too low. So I advised her to increase her dose to 10,000 units per day. Several months later, her 25-hydroxy vitamin D level: 63.8 ng/ml--perfect.
However, on hearing that she was taking 10,000 units vitamin D per day, Joanne's primary care physician was shocked: "What? Stop that immediately! You're taking a toxic dose!" So Joanne called me to find out if this was true.
No, of course it's not true. It's not the dose that's toxic, but the blood level it generates. Although it varies, vitamin D toxicity, as evidenced by increased blood calcium levels, generally does not even begin to get underway until at least 120-130 ng/ml, perhaps higher. Rarely, a dose of 2000 units per day will generate a level this high. In others, it may require 24,000 or more units per day to generate such a high level.
So it's not the dose that's toxic, but the blood level of 25-hydroxy vitamin D it generates.
Provided you and/or your doctor are monitoring 25-hydroxy vitamin D blood levels, the dose is immaterial. It's the blood level you're interested in.