COMMENTARIES

Prevalence of Metabolic Syndrome in Japanese Type 2 Diabetic Patients and Its Significance for Chronic Vascular Complications

Tokio Sanke, D.M., Ph.D., Professor and Chairman, Department of Clinical Laboratory Medicine, Wakayama Medical University, 811-1, Kimi-idera, Wakayama, 641-8509, Japan, Email: sanke-t@wakayama-med.ac.jp

The concept of the metabolic syndrome (MetS) as an independent risk factor for cardiovascular disease is recognized worldwide and several academic societies have defined their own diagnostic criteria. Type 2 diabetes mellitus produces atherosclerotic as well as microvascular changes as chronic complications and is also recognized as an independent risk factor for cardiovascular disease. Having more than one risk factor greatly increases the risk for coronary heart disease [1].

          We compared age- and duration-matched type 2 diabetic patients groups complicated with and without MetS with respect to the prevalence of macroangiopathy [myocardial infarction, brain infarction, and peripheral arterial disease (PAD: ankle-brachial blood pressure index less than 0.9)]. Contrary our expectation, the result suggests that MetS is associated with microangiopathy such as diabetic retinopathy or nephropathy rather than macroangiopathy in Japanese type 2 diabetic patients [2]. Our findings indicate that the influence of MetS on macroangiopathy might not be found in the very strong atherogenic power of type 2 diabetes itself. As patients with MetS in this study had hypertension with high prevalence (83.6% in males and 90.9% in females) which has been recognized as a risk factor for retinopathy and nephropathy, hypertension might affect the onset and development of these microvascular complications as one of the major risk factor. With respect to the macroangiopathy, there is a possibility that the patients with fetal myocardial infarction and brain infarction were dropped out and the prevalence of macroangiopathy was underestimated because our study is cross-sectional. From this perspective, PAD, and not fetal disease, may be a useful marker for such a cross-sectional study. In our study, the prevalence of PAD had also no significant difference between those with and without MetS.

We also clarified the prevalence of MetS in Japanese type 2 diabetic patients in this paper (45.9% in males and 28.0% in females). The prevalence is very low compared with that in Western countries (more than 80%). As the prevalence of MetS is largely dependent on the definition of the syndrome as well as ethnic differences, we compared the prevalence of the MetS diagnosed using the criteria proposed by the Japanese Study Group [3], IDF [4] and the NCEP-ATP III [5] in our paper. When the cut-off limit of waist circumference (≥ 85 cm in males and ≥ 90 cm in females) was employed in each set of criteria, the prevalence of MetS was increased in order of the Japanese study group, then IFD followed by the NCEP-APT criteria in both males and females [2]. This discrepancy is thought to be due to the cut-off limits of waist circumference. Much debate concerning the cut-off value and importance of waist circumference for diagnosis has arisen and the diagnostic criteria of the MetS and its impact on the cardiovascular disease should be examined among each ethnic group in the future.

          Chronic kidney disease (CKD) is reported to be an independent risk factor for cardiovascular disease as well as MetS [6]. We thus extended our study and examined the prevalence of CKD in type 2 diabetic patients and its association with macroangiopathy in comparison with those of metabolic syndrome. Part of this study was presented at the 68^th scientific session of American Diabetes Association [7] held in San Francisco, July 6-10, 2008. We used 1,005 (567 males and 438 females) Japanese type 2 diabetic patients without hemodialysis. Patients with albuminuria including microalbuminuria and/or renal function decline (eGFR less than 60 ml/min/1.73²) were diagnosed as having CKD. MetS was diagnosed using criteria proposed by the Japanese Study Group for the definition of MetS in 2005 [3]. Patients were classified into 4 groups; N group without both CKD and MetS (43.1%), M group with only MetS (23.9%), C group with only CKD (18.1%), and CM group with both CKD and MetS (14.9%). Duration and age-matched patients were selected and the prevalence of PAD were compared among the above 4 groups. The prevalence of PAD was 2.3% in N group, 3.8% in M group, 10.7% in C group, and 12.8% in CM group. This study clarifies the prevalence of CKD in Japanese type 2 diabetic patients, and indicates that CKD has more a powerful impact on macrovascular complications such as PAD than MetS in Japanese type 2 diabetic patients.

References

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2.    Shimajiri Y, Tsunoda K, Furuta M, et al. 2008. Prevalence of metabolic syndrome in Japanese type 2 diabetic patients and its significance for chronic vascular complications. Diab Res Clin Pract 79: 310-17.
3.    Study Group for the Definition of Metabolic Syndrome. 2005. Definition and diagnostic criteria of metabolic syndrome. Journal of the Japanese Society of Internal Medicine 94: 188-203.
4.    International Diabetes Federation Press Conference. 2005. The IDF consensus worldwide definition of the metabolic syndrome [article on line]. Available from http://www.idf.org/webdata/docs/IDF_Metasyndrome_definition.pdf.
5.    Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults. 2001. Executive Summary of the Third of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adults Treatment Panel III). JAMA 285: 2486-97.
6.    Weiner DF, Tighiouart H, Amin MG, et al. 2004. Chronic kidney disease as a risk factor for cardiovascular disease and all-cause mortality; a pooled analysis of community-based studies. Am J Soc Nephrol 15: 1307-15.
7.    Sanke T, Shimajiri Y, Tsunoda K, Huruta M. 2008. Prevalence of chronic kidney disease in Japanese type 2 diabetic patients and its significance for macroangiopathy in comparison with those of metabolic syndrome. Diabetes 57 (Supplement 1): A193.