Association of serum NO_x level with clustering of metabolic syndrome components in middle-aged and elderly general populations in Japan

Objectives: The aim of this study was to determine whether the serum nitrite plus nitrate (NO_x) level correlates with biomarkers that are known components of the metabolic syndrome (MetS). Methods: Serum NO_x levels were measured using a commercial kit in 608 Japanese men and women between the ages of 39 and 85 years. Multivariate adjustments for age, smoking status, alcohol consumption and exercise were made in the analysis of covariance (ANCOVA). The components of the metabolic syndrome were defined based on the following criteria: body mass index (BMI) ≥25.0 kg/m², glycated hemoglobin (HbA1c) ≥5.6%, systolic blood pressure ≥130 mmHg or diastolic blood pressure ≥85 mmHg, high-density lipoprotein-cholesterol (HDL-C) ≤1.03 mmol/l for men and ≤1.29 mmol/l for women and triglyceride ≥1.69 mmol/l. Results: The logarithmically transformed age-adjusted serum NO _x (lnNO_x) value was significantly higher in the low HDL-C group (1.76 ± 0.05 μmol/l; p < 0.05) than MetS component groups (1.65 ± 0.01 μmol/l) in men, but no difference was found in women. The means of serum lnNO_x after multivariate adjustment were 1.64, 1.65, 1.64, 1.66, and 1.81 μmol/l for 0, 1, 2, 3, and 4-5 MetS components for all subjects, respectively. The results of ANCOVA confirmed that the serum lnNO _x level was significantly correlated with the clustering of MetS components in both men and women (p < 0.0001 for trend). Conclusion: Our results suggest that an increase in the clustering of MetS components was associated with the increase in serum NO levels in our general population.