I take vitamin D as part of my brest cancer protocol. I had been taking a form that was derived from lanolin. This form gave me a pain in my liver area. It took me a long time to work out that it was the vitamin D that was causing my problem.
I changed form to a liquid one which I hold under my tongue and now can take vitamin D without any problems.
I have not noticed anything as a result of taking vitamin D. I have not experimented with it, I simply take 4000iu per day.
A blood test I had a few years ago showed my level to be '60' (quote from my NHS doctor). She told me that was too high, my hormone doctor thought that it was too low. Same country, same education opposing views.
My personal belief is it is too low, unfortunately I am working on other things in my protocol at this time and haven't been able to return to trials with vitamin D. It is on my list and I will come back to it.
One thing I am thinking is that there is much discussion about the form of vitamin D, and there is some thinking on metabolising from one form to another. It may be that I am now able to metabolise it better because my operating temperature is optimal. I haven't put a model together to test any of this yet, and I don't get enough sunshine :(