The impact of body mass index on clinical outcomes after acute myocardial infarction

Background: Several studies indicated that an elevated body mass index (BMI) is associated with a lower rate of mortality in patients with acute myocardial infarction (AMI). However, the existence of the obesity paradox in AMI patients remains controversial. Methods: We examined the association of BMI and clinical outcomes in 2157 patient with AMI (mean follow-up of 26 months). BMI was categorized into 9 groups (< 18.5, 18.5 to 20.9, 21.0 to 23.4, 23.5 to 24.9, 25.0 to 26.4, 26.5 to 27.9, 28.0 to 29.9, 30.0 to 34.9, and >= 35.0 kg/m(2)). Cox regression was used to calculate hazard ratios (HR) for the various BMI categories, adjusting for the clinical variables, left ventricular ejection fraction, and hemoglobin level. Results: BMI had a U-shaped association with mortality. Relative to the lowest mortality group (BMI of 26.5 to 27.9 kg/m(2)), the adjusted HRs for mortality were increased only in the lower (HR 2.3; 95% CI 1.3-4.2) and upper (HR 1.8; 95% 1.2-2.9) BMI categories. There was a significant interaction between BMI and anemia (P = 0.0003) such that the U-shaped relationship between BMI and mortality was present mainly in patients with anemia. Patients in the lower and upper BMI categories and concomitant anemia had a striking increase in mortality (adjusted HR 5.1, 95% CI 1.9-11.7 and 3.2, 95% CI 1.5-7.0, respectively). Conclusion: Both obesity and underweight are associated with increased mortality in patients with AMI. The risk of mortality is particularly high among underweight and obese patients with anemia. (C) 2010 Elsevier Ireland Ltd. All rights reserved.