Associations between urinary 6‐sulfatoxymelatonin excretion and diabetic vascular complications or arteriosclerosis in patients with type 2 diabetes

AIMS/INTRODUCTION: There are limited reports on the association between melatonin levels and vascular complications in patients with type 2 diabetes. The aim of this study was to determine the association between urinary 6‐sulfatoxymelatonin, which is a urinary metabolite of melatonin, and diabetic vascular complications or arteriosclerosis in patients with type 2 diabetes. MATERIALS AND METHODS: This retrospective study included patients (167 patients with type 2 diabetes and 27 patients without diabetes adjusted for age and sex) admitted to the hospital who underwent measurement of urinary 6‐sulfatoxymelatonin. The urinary 6‐sulfatoxymelatonin/creatinine ratio (6‐SMT) was calculated. RESULTS: The natural logarithmically scaled 6‐SMT level (Ln 6‐SMT) was significantly lower in type 2 diabetes patients (1.9 ± 1.1) compared with patients without diabetes (2.8 ± 1.0, P < 0.001). Multivariate linear regression analysis identified duration of diabetes, smoking status, urinary albumin‐to‐creatinine ratio, retinopathy and coronary heart disease as factors that could influence Ln 6‐SMT levels in type 2 diabetes patients (R (2) = 0.232, P < 0.001). Ln 6‐SMT was associated with decreased odds of diabetic retinopathy, even after adjustment for various confounding factors (odds ratio 0.559, 95% confidence interval 0.369–0.846, P = 0.006). Similarly, Ln 6‐SMT was associated with decreased odds of coronary heart disease (odds ratio 0.442, P = 0.030). CONCLUSIONS: Our results showed the presence of low levels of Ln 6‐SMT in type 2 diabetes patients relative to patients without diabetes. Furthermore, Ln 6‐SMT is an independent risk factor of diabetic retinopathy and coronary heart diseases. These findings suggest that 6‐SMT could be a useful biomarker for the prediction of micro‐ and macrovasculopathies in patients with type 2 diabetes.