Mortality Beyond the First Year After Spinal Cord Injury: Does Body Mass Index Matter?

Objective: To examine the association between body mass index (BMI [calculated as weight in kilograms divided by height in meters squared]) and mortality after the first year post spinal cord injury (SCI) overall and across demographic and injury characteristics.

Design: Cohort study.

Setting: Sixteen Spinal Cord Injury Model Systems (SCIMS) centers.

Participants: SCIMS Database participants age 20 years or older and having a BMI assessment during the 2007-2011 wave of data collection.

Interventions: Not applicable.

Main outcome measures: All-cause mortality rate. Life table method and log-rank test were used to estimate and compare mortality rates across BMI groups and other factors. Cox proportional hazard regression model was conducted to estimate hazard ratio (HR) and 95% confidence interval (CI).

Results: A total of 2346 participants (N=2346) with SCI were classified into 1 of the 8 BMI groups: <18.5 (6.9%), 18.5-19.9 (7.3%), 20.0-22.49 (15.0%), 22.5-24.9 (18.8%), 25.0-27.49 (17.5%), 27.5-29.9 (13.2%), 30.0-34.9 (13.5%), and ≥35.0 (7.8%). Compared with people with BMI of 22.5-29.9, a higher mortality risk was observed among people with BMI<18.5 (HR, 1.76; 95% CI, 1.25-2.49), 18.5-19.9 (HR, 1.51; 95% CI, 1.06-2.15), and ≥35.0 (HR, 1.51; 95% CI, 1.11-2.07) after adjusting for confounding factors (sex, age at the time of BMI assessment, marital status, neurologic status). The U-shape BMI-mortality relationship varied by age, sex, neurologic status, and years since injury.

Conclusions: To improve life expectancy after SCI, health care professionals could focus on weight management among patients with relatively low and extremely high BMI, defined by demographic and injury-related characteristics. Future studies should explore factors that contribute to such a higher mortality after SCI, including pre-existing conditions, poor diet and/or nutrition, and cardiorespiratory fitness.