Body Mass Index as a Prognostic Factor in Traumatic Brain Injury: Insights from a Real-World Cohort

The relationship between obesity and traumatic brain injury is complex and not fully understood. While obesity is commonly linked to worse outcomes, conflicting data support the "obesity paradox," with higher body mass index showing protective effects.

We identified patients with traumatic brain injury and defined two propensity score-matched cohorts: patients with normal weight and patients with obesity. Outcomes were compared using risk estimates, odds ratios, Kaplan-Meier survival analysis, and log-rank testing.

Obesity was associated with slightly lower risks of the following: • Pneumonia (5.1% vs. 3.4%, OR 1.53 [95% CI: 1.015-2.297], p = 0.041), • Acute kidney injury (9.3% vs. 6.8%, OR 1.41 [95% CI: 1.047-1.908], p = 0.023), • Myocardial infarction (3.4% vs. 1.7%, OR 2.04 [95% CI: 1.182-3.503], p = 0.009), • Cognitive deficits (16.9% vs. 11.9%, OR 1.52 [95% CI: 1.201-1.914], p < 0.001), • Cardiac arrest (2.5% vs. 0.8%, OR 3.05 [95% CI: 1.485-6.272], p = 0.001), • Emergency department visits or admissions (16.1% vs. 12.7%, OR 1.32 [95% CI: 1.046-1.661], p = 0.019), • Emergency procedures (16.1% vs. 11.9%, OR 1.43 [95% CI: 1.127-1.803], p = 0.003), • Twist drill/burr hole procedures (1.7% vs. 0.8%, HR 2.67 [95% CI: 1.045-6.827], p = 0.033 by log-rank test), • Mortality was not significantly different.

Patients with obesity exhibited a lower incidence of selected complications, supporting the obesity paradox in neurotrauma. However, that did not translate into differences in mortality or functional outcomes. Body mass index may not fully capture the complexities of body composition or functional reserve, highlighting the need for studies using comprehensive adiposity and metabolic measures. Given multiple outcomes tested and modest effect sizes, these findings should be interpreted cautiously.