Thanks for your reply Chiron. I think you're right- I reckon it's best to leave it, and not interfere with the natural progress of the fast.
I had a look at the vitamin D page on the site you mentioned- useful to have the facts and figures laid out for you like that.
I'm also going to be looking into the best supplemental source of D, and also a good multi, for when the fast ends. I don't have a set end date for the fast, but I want to heal my fracture to a decent level before I take food.