Adjustment for Waist Circumference Reveals a U-Shaped Association Between Glycated Hemoglobin Levels and Body Mass Index in Young Adults.

Objectives: Body mass index (BMI) is used to assess adiposity worldwide. However, additional adjustment for waist circumference (WC), a surrogate marker of abdominal fat, may be capable of revealing a latent relationship between low body weight and glycated hemoglobin (A1C) concentration. Here, we investigated the relationship between A1C and BMI in young adults, adjusting for WC.

Methods: We reviewed A1C, BMI, WC and other clinical data in a cross-sectional study of 26,475 apparently healthy Japanese people 20 to 39 years of age who were undergoing health check-ups.

Results: Although the values of most serum parameters were high in subjects with a high BMI in both younger (20 to 29 years of age, n=10,810) and older subjects (30 to 39 years of age, n=15,665), A1C had a J-shaped relationship with BMI category in younger subjects, regardless of sex. A traditional linear model via a generalized linear model showed that in younger subjects, an inverse association of A1C level with BMI category (19 to 26.9 kg/m vs. ≤18.9 kg/m) was identified after adjustment for WC. This indicates positive associations between A1C and BMI categories of ≤18.9 (beta=0.06; p<0.0001), 19.0 to 20.9 (beta=0.03; p<0.01) and ≥27.0 kg/m (beta=0.08; p<0.0001), in contrast to individuals with BMIs of 23.0 to 24.9 kg/m. Similarly, in older subjects, BMIs ≤18.9 kg/m were associated with A1C levels but to a lesser extent (beta=0.04; p<0.05) than in younger subjects.

Conclusions: Additional adjustment of BMI for WC revealed a latent U-shaped association between A1C concentration and BMI, particularly in young adults; this deserves further investigation.