Body-Mass Index and Mortality Among Adults With Incident Type 2 Diabetes

Study Questions:

Is body mass index (BMI) associated with increased mortality among adults with type 2 diabetes?

Methods:

Data from the Nurses’ Health Study (NHS) (8,970 participants) and Health Professionals Follow-up Study (PHS) (2,457 participants) were used for the present analysis. All participants were free of cardiovascular disease or cancer at the time of a diagnosis of diabetes. Body weight was updated every 2 years by questionnaire. Body weight shortly before diagnosis and height were used to calculate the BMI. Death was the primary outcome of interest.

Results:

A total of 8,970 women (from NHS) and 2,457 men (from PHS) were included. Average age at time of diabetes diagnosis was 62 years for the women and 64 years for the men. A higher BMI at diagnosis was inversely associated with age at diagnosis, physical activity, and a healthy dietary pattern. The lowest BMI category (18.5-22.4 kg/m2) had the highest prevalence of current smokers, and normal-weight participants (BMI, 18.5-24.9 kg/m2) were more likely to have lost weight before diagnosis than overweight participants (BMI, 25.0-29.9 kg/m2) and obese participants (BMI, ≥30 kg/m2). Over a mean follow-up of 15.8 years, a total of 3,083 deaths occurred. A J-shaped association was observed across BMI categories (18.5-22.4, 22.5-24.9 [reference group], 25.0-27.4, 27.5-29.9, 30.0-34.9, and ≥35.0 kg/m2) for all-cause mortality (hazard ratios [HRs] across BMI categories: 1.29, 1.00, 1.12, 1.09, 1.24, and 1.33, respectively). This relationship was linear among participants who had never smoked (HRs across BMI categories: 1.12, 1.00, 1.16, 1.21, 1.36, and 1.56, respectively), but was nonlinear among participants who had ever smoked (HRs across BMI categories: 1.32, 1.00, 1.09, 1.04, 1.14, and 1.21) (p = 0.04 for interaction). A direct linear trend was observed among participants younger than 65 years of age at the time of a diabetes diagnosis, but not among those 65 years of age or older at the time of diagnosis (p < 0.001 for interaction).

Conclusions:

The investigators concluded that there was a J-shaped association between BMI and mortality among type 2 diabetics who had ever smoked. Among never smokers, a positive relationship between BMI and mortality was observed.

Perspective:

These data shed light on why prior studies have observed mixed results regarding the relationship between BMI and all-cause mortality.

Keywords: Body Mass Index, Overweight, Diabetes Mellitus, Type 2, Body Weight, Questionnaires


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