Association of fasting glucose and glycated hemoglobin with the long-term risk of incident metabolic syndrome: Korean Genome and Epidemiology Study (KoGES)

Aims: Previous studies have proposed potential benefit of glycated hemoglobin (HbA1c) supplementary to fasting glucose in detecting metabolic syndrome (MetS). This study was to investigate an association of incident MetS with levels of HbA1c and fasting glucose. Methods: In a cohort of Korean Genome and Epidemiology Study, 5515 non-diabetic adults were grouped by the levels of baseline fasting glucose and HbA1c, and followed-up for 10 years. Using multivariate Cox proportional hazards assumption, hazards ratios (HRs) and 95% confidence interval (CI) for incident MetS (adjusted HRs [95% CI]) were calculated according to baseline fasting glucose and HbA1c. In individuals with normal fasting glucose, subgroup analysis was conducted to evaluate an association of HbA1c levels with MetS. Results: The risk for MetS significantly increased proportionally to fasting glucose ≥ 80 mg/dL and HbA1c ≥ 5.5%, compared with fating glucose < 80 mg/dL and HbA1c < 5.3%, respectively. In subgroups of normal fasting glucose, HbA1c ≥ 5.7% had the increased risk of MetS in fasting glucose < 80 mg/dL (5.7–5.9%: 1.41 [1.07–1.86] and 6.0–6.4%: 2.20 [1.40–2.92]), and HbA1c ≥ 5.5% had the increased risk of MetS in fasting glucose of 80–99 mg/dL (5.5–5.6%: 1.33 [1.08–1.64], 5.7–5.9%: 1.57 (1.27–1.93), and 6.0–6.4%: 2.37 [1.87–3.00]). Conclusions: Both elevated fasting glucose and HbA1c were significantly associated with the increased risk of MetS even within normal range. HbA1c is effective in identifying high-risk group for MetS in individuals with normal fasting glucose.