Body mass index and health status in diabetic and non-diabetic individuals

There is controversy regarding the existence of a body mass index (BMI) mortality paradox in diabetes, whereby the optimal BMI category is higher than it is in non-diabetic persons. To explore possible pathways to a mortality paradox, we examined the relationship of BMI with physical and mental health status in diabetic and non-diabetic persons.

We examined adjusted SF-12 Physical and Mental Component Summary (PCS-12 and MCS-12) scores by BMI (kg m(-2)) category (underweight, <20; normal weight, 20 to <25; overweight, 25 to <30; obese, 30 to <35; severely obese ⩾35) in adult diabetic and non-diabetic respondents to the 2000-2011 United States national Medical Expenditure Panel Surveys (N=119 161). Adjustors were age, sex, race/ethnicity, income, health insurance, education, smoking, comorbidity, urbanicity, geographic region and survey year.

In non-diabetic persons the adjusted mean PCS-12 score was highest (that is, most optimal) in the normal-weight category, whereas for diabetic persons the optimal adjusted mean PCS-12 score was in the overweight category (adjusted difference between non-diabetic and diabetic persons in the difference in PCS-12 means for overweight versus normal-weight category=0.8 points, 95% confidence interval; CI 0.1, 1.6; P=0.03). This paradoxical pattern was not evident for the MCS-12, and the adjusted difference between non-diabetic and diabetic persons in the difference in MCS-12 means for overweight versus obese persons was not significant (-0.3 points, 95% CI -0.9, 0.4; P=0.43). The findings were not significantly moderated by smoking status, cancer diagnosis or time period.

The optimal BMI category for physical health status (but not mental health status) was higher among diabetic than non-diabetic persons. The findings are consistent with a BMI physical health status paradox in diabetes and, in turn, a mortality paradox.