It has been previously thought that obesity was protective for fragility fractures, but more recent data has shown that when accounting for factors like BMD and other risk factors, the protective effect of BMI reverses on is inconclusive at some skeletal sites. Frailty is a dynamic aging condition that could be used to further understand the relationship between obesity and fracture risk. Thus, this study utilized the GLOW Hamilton, Canada cohort, which included ~4000 women. Fractures were self-reported annually, with major osteoporotic fractures (MOF) used as the primary outcome. Frailty was measured using the frailty index, which included 34 health-related deficits. Scores ranged form 0 to 1, with higher score indicating more frailty. Cox proportional hazards models were used to evaluate the association between the obesity, FI and MOF. To test if the obesity modified the association, they included a FI*obesity interaction term. They conducted a few sensitivity analyses to evaluate the robustness of their findings including: accounting for the competing risk of mortality, multiple imputation of missing data, and including all clinical fractures, except face, fingers, and toes). Among the 3985 women, 29% were obese, and the mean FI was 0.24 out of 1. Obesity alone was found to reduce the risk of fractures (HR = 0.87). In subsequent models, the obesity frailty interaction was significant, thus indicating that frailty modifies the association between obesity and fractures.

The paper was well written and provides more consistent evidence that obesity may not be protective for fragility fractures. When you think of frailty, an obese person may not be what comes to mind, but in this cohort, the frailty index was significantly higher in in obese women with fractures than without. These findings are important both clinically as well as in the research arena.

My only minor concerns are around the figures. There is not enough distinction between in color in many of the figures, particularly Figure 1 and supplemental figure 1.