Hi Hilary,
I didn't take potassium but did take some calcium for part of the time. If
you will go to this website it gives the whole story.  
http://www.celiac.com/articles/640/1/Magnesium-Helps-Rebuild-Bones-in-Celiac
-Disease-by-Ron-Hoggan/Page1.html

I found the scan to be very helpful, as I had a means of determining whether
my diet and supplements were working for me. Fortunately, because I have
celiac disease, it was easy to get my doctor to order the bone scans on both
occasions. Then he told me that my results were impossible and the second
scan had to be wrong or have been done on a different machine - but I could
see no evidence of the latter, and I could tell from how much less bone pain
I had that something had changed. I also don't feel as fragile as I did. Two
years ago, I build our retirement home and did a lot of the work myself -
and no broken bones.   

Best Wishes, 
Ron