Relation of Body Mass Index to Urinary Creatinine Excretion Rate in Patients With Coronary Heart Disease

In patients with prevalent coronary heart disease (CHD), studies have found a paradoxical relation in that patients with higher body mass indexes (BMIs) have lower mortality. One possibility is that patients with higher BMIs have greater muscle mass, and higher BMI may be a marker of better overall health status. The aim of this study was to evaluate whether the paradoxical association of BMI with mortality in patients with CHD is attenuated when accounting for urinary creatinine excretion, a marker of muscle mass. The Heart and Soul Study is an observational study of outpatients with stable CHD. Outpatient 24-hour timed urine collections were obtained. Participants were followed up for death for 5.9 ± 1.9 years. Cox proportional-hazards models were used to evaluate the association between gender-specific BMI quintiles and mortality. There were 886 participants in the study population. Participants in higher quintiles of BMI were younger, were more likely to have diabetes mellitus and hypertension, and had higher urinary creatinine excretion rate. Compared to the lowest BMI quintile, subjects in higher BMI quintiles were less likely to die during follow-up. Adjustment for major demographic variables, traditional cardiovascular risk factors, and kidney function did not attenuate the relation. Additional adjustment for urinary creatinine excretion rate did not materially change the association between BMI and all-cause mortality. In conclusion, low muscle mass and low BMI are each associated with greater all-cause mortality, but low muscle mass does not appear to explain why CHD patients with low BMIs have worse prognosis.