In a March 6, 2017 Scientific Report article, Dr. Ma (Dept. of Mechanical Engineering, Imperial College, London), et al. presented findings from a study that investigated the effects of bisphosphonate therapy on the microstructure and strength of bone. Dr. Ma looked at three cohorts of individuals from a total of 21 bone samples: 1) eight were from bisphosphonate-treated patients who
had sustained bone fractures, 2) eight were from patients who had sustained bone fractures but who had not received bisphosphonate therapy, and 3) five samples from cadavers of healthy, ageing, non-fracture individuals.
By using X-ray micro-CT and image segmentation technology, the researchers could assess both trabecular microdamage and mechanical strength of the bone samples. What they found was that bisphosphonate therapy is capable of reducing trabecular perforations (A phenomenon that weakens bones when excessive and one which I describe as "disconnected trabeculae" in my book - pages 14 and 15 - The Whole-Body Approach to Osteoporosis.) but causes an accumulation of microcracks. This abundance of microcracks (compared to the cohort that did not receive bisphosphonate therapy) lead to a loss of microstructural integrity and bone strength.
This study explains why short-term bisphosphonate use (2 years or less) can be beneficial (especially in a person with elevated osteoclastic bone resorption that is not being controlled through diet, lifestyle changes, and nutritional supplementation), but that long-term use of these drugs can be detrimental to skeletal health and strength.
The bottom line is that bisphosphonate medications can be of help in reducing immediate fracture risk in the short term but should not be used as the primary long-term treatment for osteoporosis. What SHOULD be used as primary long-term therapy for bone loss is bone-healthy nutrition and exercise, ensuring optimal GI health, and making changes in life style to promote overall health.
Ma, et al. 2017. Long-term effects of bisphosphonate therapy: perforations, microcracks and mechanical properties.
Scientific Reports DOI: 10.1038/srep43399