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"Obesity Paradox" Holds True for Patients with Hip Fracture: A Registry-Based Cohort Study
Karin Modig1, Annelie Erdefelt2, Carl Mellner3
1Unit of Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
Background:
Hip fractures are associated with high mortality and reduced quality of life. Studies have reported a high body mass index (BMI) as being positively associated with survival when linked to old age and some chronic diseases. This phenomenon is called the "obesity paradox." The association between BMI and survival after hip fracture has not been thoroughly studied in large samples, nor has to what extent the association is altered by comorbidities, sex, and age. The objective of this study was to investigate the association of BMI with survival after hip fracture and with the probability of returning to living at home after hip fracture.
Methods:
This cohort study was based on data from a prospectively maintained national registry of patients with hip fracture. A total of 17,756 patients ≥65 years of age who were treated for hip fracture during the period of 2013 to 2016, and followed until the end of 2017, were included. BMI was clinically assessed at hospital admission, comorbidity was measured with the American Society of Anesthesiologists (ASA) score, and the date of death was retrieved from a national database. Self-reported data on living arrangements were assessed on admission and 4 months after fracture. Multivariable regression models were used to estimate the associations.
Results:
Despite ASA scores being similar among all BMI groups, obese patients had the highest 1-year survival and patients with a BMI of <22 kg/m had the lowest. Adjustment for potential confounders strengthened the associations. For the chance of returning to living at home, no advantage was seen for obese patients, but patients with a BMI of <22 kg/m had clearly worse odds compared with patients who were of normal weight, overweight, or obese.
Conclusions:
The obesity paradox appears to be true for hip fracture patients aged 65 and older. Attention should be given to patients with malnutrition and underweight status rather than to those with overweight status or obesity when developing the orthogeriatric care.
Level Of Evidence:
Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.