Diabetes Q&A

HbA1c: How Much Control Is Too Much?

Glycemic variability may play a role in mortality risk among individuals aged 70 years and older with diabetes, according to a recent study.

For their study, the researchers evaluated 54,803 individuals with type 1 or type 2 diabetes. Data were obtained from the Health Improvement Network database.
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The primary outcome of the study was all-cause mortality. Hemoglobin A1c (HbA1c) was assessed in 3 models:

  • Model 1: A baseline mean HbA1c for 2003 to 2006.
  • Model 2: The mean across all of follow-up.
  • Model 3: A time-varying yearly updated mean.

Ultimately, 17,680 participants died over the course of the observation period, yielding an overall mortality rate of 77 per 1000 person-years (73 per 1000 person-years for women and 80 per 1000 person-years for men).

The researchers observed a J-shaped distribution for mortality in both men and women, with significant increases in mortality with HbA1c values greater than 8% and less than 6%.

Furthermore, increasing HbA1c variability was found to be associated with higher rates of mortality in all models. However, fitting the mean HbA1c models with the glycemic variability score altered the risk distribution, especially in model 2, which demonstrated a significantly increased mortality risk with HbA1c values greater than 9.5% in women and 9% in men.

“Both low and high levels of glycemic control were associated with an increased mortality risk, and the level of variability also seems to be an important factor, suggesting that a stable glycemic level in the middle range is associated with lower risk,” the researchers wrote.

“Glycemic variability, as assessed by variability over time in HbA1c, might be an important factor in understanding mortality risk in older people with diabetes,” they concluded.

—Christina Vogt

Reference:

Forbes A, Murrells T, Mulnier H, Sinclair AJ. Mean HbA1c, HbA1c variability, and mortality in people with diabetes aged 70 years and older: a retrospective cohort study. Lancet Diabetes Endocrinol. 2018;6(6):476-486. https://doi.org/10.1016/S2213-8587(18)30048-2