vitamin d deficiency
"Having severe bone loss, my MD put me on vitamin D2 at 50,000 units a week. My wife did the research, and found out vitamin D2 is not as well absorbed as vitamin D3. It also must be taken with a calcium supplement. I had been taking the D2 for several years, and then they wanted me to take Prolia as my bone loss was getting worse. Stopping the D2, and starting the D3 at 5,000 iu a day with 600 mg of calcium has helped quite a bit.  I would suggest anyone try this before taking something like Prolia, or Forteo for bone loss. If you have osteoporosis, you need the supplements either way. Wife took Forteo everyday for 26 months, and less than 4 years later they now want her to try Prolia too.Check wikipedia for info on this."