Nitrate and nitrite bioavailability in plasma and saliva: Their association with blood pressure - A systematic review and meta-analysis.

In this study, we conducted a systematic review and meta-analysis to determine plasma and salivary nitrate (NO) and nitrite (NO) concentrations under resting and fasting conditions in different type of individuals and their association with blood pressure levels. A total of 77 studies, involving 1918 individuals aged 19-74 years (males = 906; females = 1012), which measured plasma and/or salivary NO and NO using the chemiluminescence technique, were included. Mean plasma NO and NO concentrations were 33.9 μmol/L and 158.3 nmol/L, respectively. Subgroup analyses revealed lower plasma NO and NO concentrations in individuals with cardiometabolic risk (NO: 21.2 μmol/L; 95 % CI, 13.4-29.0; NO: 122.8 nmol/L; 95 % CI, 75.3-138.9) compared to healthy (NO: 33.9 μmol/L; 95 % CI, 29.9-37.9; NO: 159.5 nmol/L; 95 % CI, 131.8-187.1; P < 0.01) and trained individuals (NO: 43.0 μmol/L; 95 % CI, 13.2-72.9; NO: 199.3 nmol/L; 95 % CI, 117.6-281; P < 0.01). Mean salivary NO and NO concentrations were 546.2 μmol/L and 197.8 μmol/L, respectively. Salivary NO, but no NO, concentrations were higher in individuals with cardiometabolic risk (680.0 μmol/L; 95 % CI, 510.2-849.8; P = 0.001) compared to healthy individuals (535.9 μmol/L; 95 % CI, 384.2-687.6). A significant positive association (coefficient, 15.4 [95 % CI, 0.255 to 30.5], P = 0.046) was observed between salivary NO and diastolic blood pressure (DBP). These findings suggest that the health status is positively associated with plasma NO and NO concentrations, but the circulatory levels of these anions are not associated with blood pressure. Only salivary NO showed a significant positive association with DBP.