Impact of metabolic syndrome on the risk of cardiovascular disease mortality in the United States and in Japan.

The United States has a higher prevalence of metabolic syndrome (MS) and cardiovascular disease (CVD) mortality than Japan, but it is unknown how much of the difference in MS accounts for the mortality difference. The aim of this study was to examine the impact of MS on the excess CVD mortality in the United States compared with that in Japan. Data from the United States Third National Health and Nutrition Examination Survey (NHANES III; n = 12,561) and the Japanese National Integrated Project for Prospective Observation of Noncommunicable Disease and Its Trends in Aged (NIPPON DATA; n = 7,453) were analyzed. MS was defined as ≥3 of 5 risk factors (obesity, high blood pressure, decreased high-density lipoprotein cholesterol, elevated glycosylated hemoglobin, and elevated triglycerides). The results show that after a median of 13.8 years of follow-up in the United States, 1,683 patients died from CVD (11.75 per 1,000 person-years), and after a median of 15 years of follow-up in Japan, 369 patients died from CVD (3.56 per 1,000 person-years). The age-adjusted prevalence of MS was 26.7% in the United States and 19.3% in Japan. Of 5 MS factors, obesity, high blood pressure, elevated triglycerides, and glycosylated hemoglobin in the United States, and high blood pressure and elevated glycosylated hemoglobin in Japan were significant risk factors for CVD mortality. Estimates of 13.3% and 44% of the excess CVD mortality for the United States could be explained by the higher prevalence of MS and MS plus baseline CVD history than in Japan. In conclusion, the present study is the first to quantitatively demonstrate that MS and MS plus baseline CVD history may significantly contribute to the explanation of excess CVD mortality in the United States compared with Japan.