by Nicola Napoli, MD, PhD

The increasing number of older adults with obesity is a public health problem because of the increased risk of cardiovascular diseases and frailty. Growing scientific evidence suggests there is also a higher risk of fractures, especially in obese pateints at the ankle and upper leg despite normal or high bone mineral density. Several lines of research have suggested a common link between bone fragility, sarcopenia, and obesity and that aging and obesity-associated physical frailty may play a negative role on bone health. How the adverse changes in physical function and body composition in the aging and obese population contribute to bone quality and strength has not been determined. In the present study, Gregori et al., from Dr Villareal group in Houston, have looked retrospectively at the baseline assessment data of 169 older adults recruited to participate in lifestyle intervention studies. The authors used HRpQCT and finite element analyses (FEA) to determine bone quality and bone strength at both distal radius and distal tibia. Data presented in this study showed a positive correlation between bone failure load and stiffness (bone strength and quality parameters) with appendicular lean mass corrected for BMI (ALM_BMI), gait speed, grip strength, and knee extension. Moreover, multiple regression analysis revealed that ALM_BMI and grip strength were the independent predictors of stiffness and failure load at both skeletal sites. On the other hand, fat mass index (FMI) was negatively correlated with bone quality and strength.

A previous study on a mixed population of young and elderly suggested that ALM_BMI and whole body lean index are important determinants of estimated bone strength. Targeting an homogeneous population of older adults with obesity, data from Gregori contribute to identify the major determinants of bone strength using sophisticated technology and taking in account not only body composition but also physical function. The lack of aconsensus on the definition of sarcopenic obesity, did not allow authors to determine the prevalence of sarcobesity in this population.

Previous studies from Dr. Villareal's group have clearly shown that the positive effects of weight loss in elderly obese subjects on frailty are counterbalanced by a negative effect on bone mineral density and bone turnover. The effect on bone quality may be related to osteocyte function which is negatively influenced by bone unloading following weight loss. From these studies it is clear that weight loss should be always associated with physical activity in order to enhance the effects on frailty and limit bone loss.

In conclusion, these findings suggest the importance of preserving muscle mass while reducing fat mass and improving physical function to maintain bone quality and decrease the risk of fractures. The positive effects observed in this study likely will have also a positive impact on preventing falls, the major risk factor for hip fractures in the elderly.

 

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References

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