Anabolic medications directly stimulate the OsteoBlast cells that build new bone matrix. Anabolics work by increasing new bone formation faster than the OsteoClast cells can eat away the old bone. See my post about “Osteoclasts Gone Wild”.
Bone matrix is the protein part of bone. The amount of bone matrix determines the size, thickness and internal structure of the bone. If there is too little bone matrix, the bone will be weak no matter how much calcium it contains. Anabolics increase the amount of bone matrix available for calcium to bind to.
If you have fractured, you have already proven that your bone is not strong enough. It is time to increase not just the amount of calcium in the bone. It is time to increase the amount of bone matrix to strengthen the bone with new structure. Anabolics add, thicken, and strengthen new struts in spongy bone. Anabolics thicken cortical (dense, often hollow cylinder) bone on both the inner and outer surfaces.
How can we tell if an Anabolic is a good choice? A very low Bone Mineral Density, or a falling BMD while on another type of medication, is one indication. A Fragility Fracture, especially a hip fracture or Vertebral Compression Fracture detected by Vertebral Fracture Assessment, is a very good indication. A hip or vertebral fragility fracture makes the diagnosis of Osteoporosis.
Anabolics add new bone matrix to all surfaces of the bone already present. Anabolics build new struts in spongy bone. Both of these actions strengthen bone. Gradually patients add calcium to the new bone matrix and gain Bone Mineral Density as well. This strengthens bone further. Of course, and I cannot stress this too much, you must consume enough Calcium and Vitamin D for any medication to work.
Antiresorptives preseve bone by decreasing bone turnover in both resorption and formation. Anabolic medications increase total bone by increasing bone turnover with the scale tipped toward bone formation.
All currently approved Anabolics are a portion of human parathyroid hormone given once daily. Forteo is the one approved in the USA.
Jay Ginther, MD
2008 / Revised Feb 2011