The impact of body mass index on mortality rates of hip fracture patients: a systematic review and meta-analysis.

Obesity has been recognized as a global epidemic as approximately one-third of the world's population. Findings on early and late mortality rates between obese, overweight, and underweight vs normal body mass index (BMI) patients confirm that the obese and overweight patients were found to have lower risk and underweight patients were found to have increased risk of mortality as compared to normal weighted patients. It is unclear if the "obesity paradox" exists with survival outcomes of hip fracture patients. We hereby reviewed early (in-hospital and 30-day mortality) and late mortality (≥ 1-year) rates between obese, overweight, and underweight vs normal body mass index (BMI) patients with hip fractures. PubMed, Embase, ScienceDirect, CENTRAL, and Google Scholar were searched for studies reporting mortality rates of hip fracture patients based on BMI. We pooled crude and adjusted mortality rates in a random-effects model. Eleven studies were included. Meta-analysis indicated significantly reduced risk of early (RR: 0.64 95% CI: 0.59, 0.69 I2 = 0% p < 0.00001) and late mortality rates (RR: 0.78 95% CI: 0.67, 0.91 I2 = 93% p = 0.002) in obese vs normal BMI patients. Meta-analysis failed to demonstrate any statistically significant difference in early mortality (RR: 0.90 95% CI: 0.54, 1.53 I2 = 44% p = 0.71) but significantly reduced risk of late mortality in overweight vs normal BMI patients (RR: 0.85 95% CI: 0.73, 0.93 I2 = 84% p = 0.003). Scarce data suggested increased risk of early (RR: 1.44 95% CI: 1.08, 1.93 I2 = 26% p = 0.01) and late mortality (RR: 1.23 95% CI: 1.08, 1.41 I2 = 7% p = 0.002) in underweight vs normal BMI patients. Adjusted data corroborated the reduced risk of mortality in overweight (HR: 0.78 95% CI: 0.74, 0.83 I2 = 0% p < 0.0001) and obese patients (HR: 0.66 95% CI: 0.60, 0.73 I2 = 0% p < 0.0001). Our results indicate that the "obesity paradox" exists with survival outcomes of hip fracture patients. Obese and overweight patients were found to have lower risk and underweight patients were found to have increased risk of mortality as compared to normal weighted patients.