Abstract 006: Fitness Status Influences the Paradoxical Association Between BMI and Mortality Risk
Introduction: In some populations, recent evidence supports a higher mortality risk in individuals with relatively low body mass index (BMI), and lower risk in some overweight or obese individuals. However, the role of fitness in this puzzling relationship, termed as the obesity paradox, has not been fully explored.
Hypothesis: We assessed the hypothesis that fitness attenuates the BMI-mortality risk paradoxical association.
Methods: The association of exercise capacity and mortality risk in 18,228 individuals (mean age: 58±11) was assessed. Three fitness categories were formed based on the 33rd and 66th percentiles of exercise capacity (METs) achieved: Low-Fit (≤6 METs; n=6,072); Moderate-Fit: 6.1-8.5 METs; n=6,158); and High-Fit: >8.5 METs; n=5,998). Individuals were also classified based on BMI as Normal-Wt (BMI 18.5-24.9); Over-Wt (BMI: 25-29.9); Moderate-Obese (BMI: 30-34.9) and Obese (BMI ≥35).
Results: There were 4,770 deaths (median follow-up 10.1 years). After controlling for age, risk factors and medications, we observed a paradoxical association between BMI categories and mortality risk (p<0.001 for trend). We also observed an inverse and graded association between fitness status and mortality for the entire cohort and within BMI categories, with reductions in risk ranging from approximately 30% to 60% (p<0.001). We then assessed mortality risk based on fitness status within each BMI category, using the Normal-Wt/High-Fit individuals as the reference group. A paradoxical BMI-mortality risk association was evident in all fitness categories. However, in Low-Fit individuals the risk was significantly increased within each BMI category (hazard ratios (HR): 2.26; 1.7; 1.7 and 1.76 for Normal-Weight, Over-Wt; Moderate-Obese and Obese categories, respectively; p<0.001 for all comparisons). However, in Moderate-Fit individuals, a significantly higher risk was observed only in the Normal-Wt category (HR: 1.58; p<0.001). Finally, in High-Fit individuals, mortality risk was significantly lower in Over-Wt (HR: 0.79; p=0.03) and Moderately Obese categories (HR: 0.58; p<0.001).
Conclusions: These findings suggest that the paradoxical association between BMI and mortality risk is strongly modulated by fitness status.
- © 2013 by American Heart Association, Inc.