Melatonin's potential preventive effect against cardiovascular disease (CVD) remains hypothetical. No study has evaluated the relationships between endogenous melatonin and the established blood biomarkers related to CVD. The objective of the present study is to examine the association between the endogenous melatonin level and various established blood biomarkers of risk of CVD, including white blood cell (WBC) count and plasma concentrations of lipids, homocysteine, uric acid (UA), and high-sensitivity C-reactive protein (hs-CRP). This cross-sectional study included 181 Japanese women who attended a health checkup program provided by a general hospital between March 2005 and March 2006. All study subjects responded to a self-administered questionnaire and were measured for weight, height, and blood pressure. Venous fasting blood and first-void morning urine were obtained from all subjects. Statistically significant inverse correlations were observed between urinary 6-sulfatoxymelatonin (aMT6s), the major metabolite of melatonin in urine, and WBC count, UA, and hs-CRP after controlling for age, body mass index, menopausal status, smoking status, diet, sleeping habits, and exercise (r = -0.19, -0.21, and -0.24, respectively). There were no significant correlations between urinary aMT6s and plasma lipids and homocysteine. These data suggested that the urinary aMT6s level was inversely associated with established independent risk factors for CVD, such as WBC, UA, and hs-CRP. Endogenous melatonin may have implications for the risk of CVD.
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