Seasonal variation in metabolic syndrome prevalence.

Accumulating evidence has shown that seasonal variations can exist within metabolic syndrome parameters. The aim of this study was to examine the hypothesis that there are seasonal variations in the prevalence of metabolic syndrome in Japanese subjects. We investigated a total of 1202 male workers in our institution (44+/-10 years) who underwent health checkups in both June (summer) and December (winter) 2008. In this study, metabolic syndrome was defined according to the criteria proposed by the National Cholesterol Education Program (NCEP), the International Diabetes Federation (IDF) and the Japanese Society of Internal Medicine (JSIM). Serum levels of high-density lipoprotein-cholesterol and fasting glucose, as well as blood pressure (BP), were significantly higher in winter than in summer, whereas waist circumference and serum levels of triglyceride exhibited little change. The prevalence rates of NCEP, IDF, and JSIM metabolic syndrome in this study were 3.8, 15.1 and 12.4% in winter and 3.2, 10.7 and 8.4% in summer, respectively. Of all metabolic syndrome components, an elevated BP was most significantly correlated with the seasonal variation of metabolic syndrome prevalence. This study demonstrated seasonal variations in metabolic syndrome prevalence in Japanese male workers. These results indicate that the season of health checkups may affect the clinical diagnosis and management of metabolic syndrome.