No “Obesity Paradox” in Type 2 Diabetes

In contrast to some previous reports, higher body mass index (BMI) is associated with increased mortality among patients with type 2 diabetes, concludes a study in the New England Journal of Medicine.

The researchers analyzed prospective follow-up data from 8970 women and 2457 men with type 2 diabetes, drawn from the Nurses’ Health Study and the Health Professionals Follow-up Study, prospectively. When the cohort members received diagnoses of diabetes, all were free of known cardiovascular disease and cancer. Prediagnosis BMI was analyzed as a predictor of long-term mortality. The analysis included 3083 deaths over an average follow-up time of 15.8 years.

Among all individuals with type 2 diabetes, there was a J-shaped association between all-cause mortality and BMI. Hazard ratio (HR) for death was 1.29 at a BMI of 18.5 to 22.4, compared with the reference category of 22.5 to 24.9. The HR then increased to 1.12 at a BMI of 25.0 to 27.4, 1.09 at 27.5 to 29.9, 1.24 at 30.0 to 34.9, and 1.33 at 35.0 or higher.

Among never-smokers, the HRs for all-cause mortality increased in linear fashion with BMI: HR 1.12 at a BMI of 18.5 to 22.4, 1.16 at 25.0 to 27.4, 1.21 at 27.5 to 29.9, 1.36 at 30.0 to 34.9, and 1.56 at 35.0 or higher. For individuals who had ever smoked, the association was nonlinear: HR 1.32, 1.09, 1.04, 1.14, and 1.21, respectively. Mortality increased in linear fashion for individuals younger than 65 years at diagnosis of diabetes but not for those who received their diagnoses at 65 or older.

Some studies have reported an apparent “obesity paradox” in type 2 diabetes, with lower mortality among obese or overweight patients compared with those of normal weight. These prospective cohort data show a J-shaped association between BMI and mortality, overall and for patients with any history of smoking. For those who have never smoked, the risk of death increases in direct linear fashion with BMI. “We did not observe a benefit of excess adiposity with regard to the risk of death,” the researchers write; “thus, our findings support the current recommendation that patients with diabetes achieve or maintain a normal weight” [Tobias DK, et al. Body-mass index and mortality among adults with incident type 2 diabetes. N Engl J Med 2014; 370:233–244].

March 2014 (Vol. 6, Number 3)