Body mass index as a risk factor for coronary events and mortality in patients with type 1 diabetes

Objective To investigate the potential relationship between body mass index (BMI) and the risk for myocardial infarction and coronary death in patients with type 1 diabetes. Methods We studied patients with type 1 diabetes included in the Swedish National Diabetes Registry during 2002-2004 and followed them until a discharge diagnosis for myocardial infarction, acute coronary event, death or until 31 December 2011. Cox regression was used to estimate relative risks. Results In 17 499 patients with type 1 diabetes (mean age 39.4 years; mean BMI 25.2 kg/m(2)), 819 were diagnosed with myocardial infarction as a primary or secondary diagnosis during a mean follow-up of 8.5 years (maximum 9.9 years). Estimated with Cox regression, there was no significant effect of increased BMI on the risk of myocardial infarction (HR 1.4 (95% CI 0.7 to 2.5) in the group with BMI >35 kg/m(2) compared with BMI 18.5-25 kg/m(2). There was no association between BMI and coronary mortality, acute coronary events or all-cause mortality after adjusting for other known risk factors. Underweight patients (BMI <18.5 kg/m(2)) had increased hazard for coronary (HR 5.0 (95% CI 1.5 to 16.9)) and all-cause mortality (HR 5.4 (95% CI 3.1 to 9.6)) compared with BMI 18.5-25 kg/m(2). Conclusions Among patients with type 1 diabetes, increased BMI is not a significant independent risk factor for myocardial infarction or coronary death after adjustment for other risk factors. Low BMI (less than 18.5 kg/m(2)) is associated with mortality from coronary or any cause.