I would be very careful with recommending vit D like this like the new miracle. We have had a say at this forum; something like; when every doctor recommends it; do opposite. It is a reason for it.
I have a truck load of collegues in the medical field, all vit D deficient. Very few if any had any effect of it.
There are other factors in here, iodine, hypo T for a start, but something about the enzymes too, I believe.