High normal HbA1c levels were associated with impaired insulin secretion without escalating insulin resistance in Japanese individuals: the Toranomon Hospital Health Management Center Study 8 (TOPICS 8)

Publisher Website
Google Scholar
Abstract
Diabet. Med. 29, 1285–1290 (2012) Abstract Aims We aimed to characterize the association of insulin resistance, impaired insulin secretion and β‐cell dysfunction in relation to HbA1c levels in a non‐diabetic range in Japanese individuals without clinically diagnosed diabetes. Methods This cross‐sectional study included 1444 individuals without a history of outpatient treatment of diabetes or use of insulin or oral hypoglycaemic agents. The homeostasis model assessment of insulin resistance and beta‐cell function, insulinogenic index, Matsuda index and disposition index were calculated using data from 75‐g oral glucose tolerance tests and compared across quintile (Q) categories of HbA1c levels. Results Fasting plasma glucose and 30‐min and 60‐min plasma glucose (PG) levels were significantly higher when HbA1c exceeded 36 mmol/mol (5.4%). A HbA1c concentration of 36–37 mmol/mol (5.4–5.5%) (Q3) was significantly associated with a 15% lower homeostasis model assessment of β‐cell function value and 31% lower insulinogenic index value compared with HbA1c ≤ 32 mmol/mol (≤ 5.1%) (Q1) (P 1c concentration of 38–40 mmol/mol (5.6–5.8%) (Q4) was associated with 17% (P P 1c exceeded 41 mmol/mol (5.9%). Individuals with HbA1c ≥ 41 mmol/mol (≥ 5.9%) (Q5) had a 69% lower disposition index than those with a HbA1c concentration of ≤ 32 mmol/mol (≤ 5.1%) (Q1). Conclusions Elevated HbA1c levels ≥ 41 mmol/mol (≥ 5.9%) were associated with substantial reductions in insulin secretion, insulin sensitivity and β‐cell dysfunction in Japanese individuals not treated for diabetes. High normal HbA1c levels of 36–40 mmol/mol (5.4–5.8%) were also associated with impaired insulin secretion without marked insulin resistance in Japanese individuals.