There is a recognizable U-shaped relationship between body mass index (BMI) and all-cause mortality in African American and white patients with type 2 diabetes, with increased risk of all-cause mortality particularly observed among African Americans with BMI <30 kg/m2 and BMI ≥35 kg/m², and among whites with BMI <25 kg/m² and BMI ≥40 kg/m² compared with patients with BMI 30-34.9 kg/m², according to a study published Nov. 5 in Circulation.

Additional Resources CardioSmart for Your Patients: About Type 2 Diabetes

Long associated with the development of type 2 diabetes – with approximately 45 to 65 percent of patients with the disease qualified as obese in the U.S. – the relationship between BMI and mortality among these patients has continued to be unclear. With previous studies providing supportive information of inverse associations, positive associations, U-shaped associations, and even no associations between BMI and mortality among patients with diabetes, Wenhui Zhao, MD, PhD, Pennington Biomedical Research Center, Baton Rouge, LA, and colleagues sought to examine the race-specific association between different levels of BMI at baseline and during follow-up with the risk of all-cause mortality among patients with type 2 diabetes.

Performing a prospective cohort study on 19,478 African American and 15,354 white patients with type 2 diabetes, Cox proportional hazards regression models were used to estimate the association of different levels of BMI stratification with all-cause mortality. During a mean follow-up of 8.7 years, results identified 4,042 deaths. The multivariable-adjusted (age, sex, smoking, income and type of insurance) hazard ratios for all-cause mortality associated with BMI levels (18.5-22.9, 23-24.9, 25-29.9, 30-34.9, 35-39.9, and ≥40 kg/m²) at baseline were 2.12 (95 percent confidence interval [CI] 1.80-2.49), 1.74 ( 1.46-2.07), 1.23 (1.08-1.41), 1.00, 1.19 (1.03-1.39), and 1.23 (1.05-1.43) for African Americans, and 1.70 (1.42-2.04), 1.51 (1.27-1.80), 1.07 (0.94-1.21), 1.00, 1.07 (0.93-1.23), and 1.20 (1.05-1.38) for whites, respectively. Stratified by age, smoking status, patient types or use of anti-diabetic drugs, results showed that a U-shaped association was still present. When BMI was included in the Cox model as a time-dependent variable, the same U-shaped association remained.

“Potential explanations of this U-shaped association among patients with diabetes are unclear,” the authors conclude. “For the negative part of the curve, the increased risk of death associated with a low BMI, some investigators have suggested that patients with low-normal weight are associated with a clinical sign of insufficient insulin secretion which could potentially lead to faster progression of nephropathy and subsequently, increased mortality. For the positive part of the curve, the increased risk of death associated with a high BMI, many previous studies among patients with diabetes failed to show it because of the small sample size which limited the statistical power when the analysis was focused on those who are extreme obese, like BMI ≥40 kg/m².”

They add that “Obesity is a well-established risk factor for numerous chronic diseases and adipose tissue can release a large number of cytokines and bioactive mediators which play important roles in the pathogenesis of many obesity related cardiovascular diseases.”

Keywords: Follow-Up Studies, Thinness, Body Mass Index, African Americans, Cytokines, Diabetes Mellitus, Type 2, European Continental Ancestry Group, Risk Factors, Obesity, Confidence Intervals, Insulins

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