Relationship between mortality and BMI after fracture: a population-based study of men and women aged ≥40 years

Fractures in obese older individuals contribute significantly to the overall burden on primary health care, but data on their impact on mortality are lacking. We studied the association between obesity and mortality following hip and nonhip clinical fractures in a retrospective, population-based cohort study. The Sistema d'Informació pel Desenvolupament de la Investigació en Atenció Primària (SIDIAP(Q) ) database contains primary care computerized medical records of a representative sample of >2.1 million people (35% of the population) in Catalonia (Spain), linked to hospital admissions data. We included in this analysis anyone aged 40 years and older suffering a hip or nonhip clinical fracture in 2007 to 2009 in the SIDIAP(Q) database. The main exposure was the most recent body mass index (BMI) measured before fracture, categorized as underweight (<18.5 kg/m2), normal (18.5 to <25 kg/m2 ), overweight (25 to <30 kg/m2), and obese (≥30 kg/m2). Furthermore, the study outcome was all-cause mortality in 2007 to 2009 as provided to SIDIAP(Q) by the National Office of Statistics. Time to death after fracture was modeled using Cox regression. Multivariate models were adjusted for age, gender, smoking, alcohol intake, oral glucocorticoid use, and Charlson comorbidity index. Within the study period, 6988 and 29,372 subjects with a hip or nonhip clinical fracture were identified and followed for a median (interquartile range) of 1.17 (0.53-2.02) and 1.36 (0.65-2.15) years, respectively. Compared to subjects of normal weight, adjusted hazard ratios (HRs) for mortality in overweight and obese subjects were 0.74 (95% CI, 0.62-0.88; p = 0.001) and 0.74 (95% CI, 0.60-0.91; p = 0.004) after hip and 0.50 (95% CI, 0.32-0.77; p = 0.002), 0.56 (95% CI, 0.36-0.87; p = 0.010) after nonhip fracture. In conclusion, the highest mortality was observed in individuals with low BMI, but compared to subjects of normal weight, obese and overweight individuals survived longer following fracture. The latter observation is consistent with data reported in other chronic conditions, but the reasons for reduced mortality in obese and overweight subjects when compared to those of normal weight require further research.