The Cutoff Value of Fasting Plasma Glucose to Differentiate Frequencies of Cardiovascular Risk Factors in a Korean Population

Diabetes and impaired glucose tolerance (IGT) are associated with increased cardiovascular mortality. Almost all studies, however, failed to detect evidence of the presence of a fasting plasma glucose (FPG) threshold for risk of cardiovascular disease that would clearly identify groups with a low or high risk (1,2). Some studies suggested that an FPG of 5.4–5.7 mmol/l has been found to be closer to a 2-h cutoff of 7.8 mmol/l both in terms of the sensitivity for future diabetes and in defining a category of similar prevalence to IGT (3,4). The interrelationships between cardiovascular risk factors and glucose levels may vary between different populations. Therefore, these findings need to be tested in other populations with different environmental and genetic backgrounds.

The medical records of 54,623 subjects (30,435 men and 24,188 women) who attended the Health Promotion Center in the Samsung Medical Center between 1998 and 2001 were examined for this analysis. Obesity was defined as a BMI ≥27 kg/m². Hypertension was defined as systolic blood pressure ≥140 mmHg, diastolic blood pressure ≥90 mmHg, and/or the current use of antihypertensive drugs. Dyslipidemia was defined as LDL cholesterol ≥4.1 mmol/l, triglycerides ≥2.46 mmol/l, HDL cholesterol <1.04 mmol/l, and/or current use of antilipid drugs. Cases of previous history of diabetes were excluded.

All study subjects were classified into 12 groups according to FPG (10 deciles of normal fasting glucose [NFG]: NFG 1, −4.56, n = 5,370; NFG 2, 4.57–4.72, n = 4,495; NFG 3, 4.73–4.89, n = 6,321; NFG 4, 4.90–5.00, n = 4,655; NFG 5, 5.01–5.11, n = 4,841; NFG 6, 5.12–5.22, n = 4,503; NFG 7. 5.23–5.33, n = 4,233; NFG 8, 5.34–5.50, n = 5,236; NFG 9, 5.51–5.72, n = 4,926; NFG 10, 5.73–6.09, n = 4,230, IFG, 6.10–6.99, n = 3,587; and diabetes, 7.00 mmol/l, n = 2,226). Those with an FPG ≤4.56 mmol/l formed the lowest group, and those with FPG >7.0 mmol/l formed the highest group. Frequencies of obesity in each group were 5.2, 6.7, 8.2, 8.9, 9.2, 10.9, 11.1, 12.9, 14.5, 17.0, 19.0, and 20.3%, respectively. Those of hypertension were 11.3, 13.2, 15.0, 16.6, 18.2, 20.1, 22.9, 23.2, 27.4, 32.8, 37.8, and 37.4%, respectively. Finally, those of dyslipidemia were 25.0, 29.0, 31.5, 34.7, 36.3, 39.3, 41.7, 42.6, 47.5, 52.8, 58.6, and 67.0%, respectively. After controlling for age and sex and odds ratio (OR) for obesity, hypertension and dyslipidemia in the IFG group were 4.04 (3.43–4.75), 2.80 (2.48–3.17), and 2.74 (2.47–3.04), respectively, with FPG subjects ≤4.56 mmol/l (NFG1) as the referent group. Those in the diabetes group were 4.29 (3.59–5.13), 2.65 (2.31–3.04), and 4.13 (3.66–4.67) (Fig. 1). Although there was no clear cutoff point to differentiate the risk of obesity, a threshold at an FPG value of 5.34–5.50 mmol/l was suggested. For hypertension and dyslipidemia, more clear threshold values were observed. The group with an FPG value of 5.51–5.72 mmol/l had a considerably greater OR of hypertension and dyslipidemia than the group with an FPG value of 5.34–5.50 mmol/l.

The data clearly showed that even in the NFG range, the level of fasting glucose was closely related to the frequencies of cardiovascular risk factors, including obesity, hypertension, and dyslipidemia, and strongly suggested the significance of a concentrated effort to reduce the cardiovascular risk factors in the earlier stage of an FPG <6.10 mmol/l in a Korean population.