Optimal Cut Points of Waist Circumference for the Clinical Diagnosis of Metabolic Syndrome in the Japanese Population

RESEARCH DESIGN AND METHODS—

We reviewed cross-sectional data from 1,658 men and 1,116 women (aged 48.8 ± 9.8 and 46.8 ± 10.4 years, respectively) who had annual medical checkup services provided by their employers. The medical checkup took place from May 2005 to November 2006 at the Human Dry Dock Center Wellness in Fukuoka, Japan. Subjects on antihypertensive and/or antidiabetic medications were included as individuals with hypertension and/or diabetes, respectively. We excluded 158 subjects on medications for dyslipidemia because we were unable to determine whether they were treated for hypercholesterolemia or hypertriglyceridemia. The study protocol was approved by the ethics committee of the related institutes.

Measurements

Waist circumference was measured at the level of the umbilicus. Blood pressure was measured at rest using an automatic sphygmomanometer. All blood samples were withdrawn after an overnight 10-h fast. Mean carotid intima-media thickness (IMT) was measured by ultrasonography (SDU-2200; Shimadzu, Kyoto, Japan) equipped with IMT measurement software (Intimascope; Media Cross, Tokyo, Japan) (8).

Definitions of metabolic syndrome

We diagnosed metabolic syndrome by each waist cut point and two or more of the following risk factors: using the IDF definition, 1) blood pressure, systolic ≥130 and/or diastolic ≥85 mmHg, 2) triglycerides ≥150 mg/dl, 3) HDL cholesterol <40 mg/dl in men and <50 mg/dl in women, and 4) fasting plasma glucose ≥100 mg/dl; and using the Japanese definition, 1) blood pressures, same as the IDF, 2) triglycerides ≥150 mg/dl and/or HDL cholesterol <40 mg/dl, and 3) fasting plasma glucose ≥110 mg/dl.

Statistical analyses

Receiver operating characteristic (ROC) curve analyses were performed using Dr. SPSS II 11.0.1J software (SPSS Japan, Tokyo, Japan), and the optimal cut points were obtained from the Youden index, maximum (sensitivity + specificity − 1) (11) (12). ANOVA and multiple comparisons were used to compare carotid IMT among subject groups for statistical significance and were performed using StatView software (SAS Institute, Cary, NC). Statistical significance was inferred at P < 0.05.

RESULTS—

We plotted ROC curves to determine optimal waist cut points (87 cm in men and 80 cm in women) to identify subjects with multiple risk factors with maximum sensitivity and specificity using the Youden index for both of the definitions (Fig. 1A–D). Using the optimal cut point of 87 cm for men, the sensitivity and specificity were 68 and 62% for the IDF and 70 and 57% for the Japanese definition, whereas the cut point of 90 cm, compared with 87 cm, showed lower sensitivity of 51% for the IDF and 53% for the Japanese definition (Fig. 1A and B). Using the optimal cut point of 80 cm for women, the sensitivity and specificity were 74 and 70% for the IDF and 84 and 68% for the Japanese definition. The former IDF and Japanese cut point of 90 cm showed inadequate sensitivity of 33% for the IDF and 38% for the Japanese definition (Fig. 1C and D).

Next, we divided the subjects into subgroups by waist circumference. In men, the cut points of 85, 87, and 90 cm identified 25.0, 21.9, and 16.2% of subjects with the metabolic syndrome, respectively, for the IDF definition and 14.9, 13.4, and 10.2%, respectively, for the Japanese definition. In subgroups with abdominal adiposity, IMT increased significantly in metabolic syndrome subjects with multiple risk factors, suggesting feasibility of the cut points of 85, 87, and 90 cm (Fig. 1E and F). With any of the above cut points, the increasing IMT in metabolic syndrome subjects was more specific using the Japanese definition (Fig. 1E and F).

In women, the cut points of 80 and 90 cm identified 7.0 and 3.0% of metabolic syndrome subjects, respectively, for the IDF definition and 2.8 and 1.3% of subjects, respectively, for the Japanese definition. In subjects with waist circumference ≥90 cm, there was no significant difference in IMT using either definition. In contrast, when we used the cut point of 80 cm, the IMT increased significantly in metabolic syndrome subjects (Fig. 1G and H), suggesting the feasibility of the optimal cut points (80 cm) and the revised IDF definition. The increasing IMT in metabolic syndrome subjects was more specific using the IDF definition (Fig. 1G and H).

The optimal cut points obtained in the present study, 87 cm for men and 80 cm for women, predicted increasing IMT in metabolic syndrome subjects. These cut points were equivalent to those in a previous report by Hara et al. (4) that proposed ∼85 cm for men and ∼80 cm for women.

Finally, a potential limitation of this study is that the subjects were exclusively company employees who may not represent the whole Japanese population. Another metabolic syndrome definition, which includes waist criteria as an optional component, was proposed by the American Heart Association/National Heart, Lung and Blood Institute (13). Including requisiteness of waist circumference, further studies are required to optimize metabolic syndrome definitions in larger populations.

CONCLUSIONS—

The optimal waist cut points were 87 cm for men and 80 cm for women. These cut points not only had maximum sensitivity and specificity to identify subjects with multiple risk factors but also predicted increased IMT in metabolic syndrome subjects. In men, both definitions were feasible. However, the Japanese definition (85 cm) surpasses the IDF definition (90 cm), since the cut point of 90 cm decreased sensitivity. In women, only the IDF definition (80 cm) was feasible to identify metabolic syndrome subjects in Japanese population.