It is well established that thalassemia does cause osteo issues in the more severe forms of thal. I would imagine, like with most other issues, that it is a gray area in thal minor, but that thal minor is likely involved, due to diminished oxygen to the bone marrow.
In addition to the obvious vitamin D and calcium, both magnesium and vitamin B-12 are essential for bone growth. The discovery of the B-12 connection is rather recent, so many doctors are not aware of this. Studies have also shown that thal minors do better when their B-12 level is near the high end of normal. Research has also showed that vitamin D is much better absorbed when magnesium is also taken. I would also advise natural vitamin E for its ability to improve circulation and help deliver oxygen to tissue.