Differential associations between body mass index and outcome in different age groups in patients with myocardial infarction

To investigate the association between age and body mass index (BMI) and mortality in patients with myocardial infarction (MI). Methods We divided 6453 patients into three age groups (<60, 60–75, >75 years) and five BMI categories. Thirty-day and long-term all-cause mortality were assessed. No association was found between the BMI category and 30-day mortality in any age group. The association between BMI and long-term multivariable-adjusted mortality risk was age-dependent. Overweight patients had a lower risk than patients with BMI <25 kg/m2 in all age groups (HR 0.62; 95%CI 0.45–0.85; p = 0.003, HR 0.78; 95%CI 0.65–0.93; p = 0.005, HR 0.82; 95%CI 0.70–0.95; p = 0.011 for ages <60, 60–75, >75 years, respectively). The lower risk of death as a function of BMI shifted upward with age, and the risk was also lower in patients with obesity grade I (HR 0.81; 95% CI 0.66–0.98; p = 0.035 and HR 0.78; 95% CI 0.63–0.97; p = 0.023 for ages 60–75, >75 years, respectively). Excessive obesity was harmful only in the oldest group. Patients with obesity grade III had more than a 2.5 times higher mortality risk than patients with BMI <25 kg/m2 only in this group (HR 2.58; 95%CI 1.27–5.24; p = 0.009). An obesity paradox was found in all age groups. Our results suggest that moderate weight gain with age improves long-term survival after MI and that the magnitude of this “protective” weight gain is greater in older compared to younger patients. However, excessive weight gain (obesity grade III) is particularly harmful in the oldest age group. The exact relationship between BMI, age, and mortality remains unclear.