1) Calcium doesn't cause or aggravate afib. I have afib and take calcium. Your doc may have wanted to you to avoid too much calcium supplementation because the latest advice is to get it from food, unless allergic to dairy. The idea is too much calcium can end up in the lining of blood vessels not in bones. (Vitamins D and K help with this.) You need 800-1200mg calcium each day, from food and then supplements if still needed, according to all of my docs.

2)Letrozole does not destroy calcium. It eliminates estrogen coming from the adrenal glands after menopause, basically eliminating estrogen in our body.

3) Letrozole does not cause tibia and hip breakage specifically. Are you taking Reclast? That may be what you are thinking of. The tibia and femur fractures are a risk after several years on Reclasst.

4) Letrozole dose cause bone density to go down, due to estrogen deprivation, so Reclast is often prescribed with it, an infusion that affects bone turnover and also may help with cancer, according to some (this is controversial I think).

5) If bone density goes down, fractures are possible, in the spine or anywhere else. But Reclast seems to help with this,

6) You have not been on letrozole long enough for severe bone loss. It is likely you already had osteoporosis before starting it. What are your DEXA scores for spine and hip?