A Literature Review on the Waist Circumference Criteria for Metabolic Syndrome in Japan: Evidence and Implications...

Waist circumference (WC) is widely used as a marker of central obesity in the diagnosis of metabolic syndrome (MetS) and it plays an important role in cardiovascular disease (CVD) risk screening. In Japan, the MetS diagnostic criteria established in 2005 require abdominal obesity as a mandatory component, with WC cutoff values of 85 cm for men and 90 cm for women. These criteria are also applied in the national Specific Health Checkup and Specific Health Guidance programs to identify individuals at a high risk of CVD. However, the scientific basis and clinical implications of these thresholds remain controversial.This review summarizes the epidemiological evidence on WC cutoff values in the Japanese population and their relevance to CVD risk. A literature search of PubMed and Ichushi-Web identified studies examining WC thresholds in relation to visceral fat accumulation, clustering of cardiometabolic risk factors, and incident CVD. The evidence was organized into four themes: (1) WC cutoffs based on visceral fat area, (2) prediction of cardiometabolic risk factor clustering, (3) the association between WC and incident CVD, and (4) associations between MetS definitions and CVD risk.Available evidence suggests that the WC thresholds corresponding to visceral fat accumulation and cardiometabolic risk clustering are generally lower than the current Japanese criterion for women. Prospective studies examining WC alone have reported inconsistent associations with incident CVD, particularly among women. Overall, the evidence suggests that CVD risk stratification frameworks requiring abdominal obesity based on WC thresholds may have limitations. Future screening strategies in Japan may benefit from greater emphasis on clustering and the overall burden of cardiometabolic risk factors.