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

In this study, we conducted a systematic review and meta-analysis to determine plasma and salivary nitrate (NO₃^-) and nitrite (NO₂^-) 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 NO₃^- and NO₂^- using the chemiluminescence technique, were included. Mean plasma NO₃^- and NO₂^- concentrations were 33.9 μmol/L and 158.3 nmol/L, respectively. Subgroup analyses revealed lower plasma NO₃^- and NO₂^- concentrations in individuals with cardiometabolic risk (NO₃^-: 21.2 μmol/L; 95 % CI, 13.4-29.0; NO₂^-: 122.8 nmol/L; 95 % CI, 75.3-138.9) compared to healthy (NO₃^-: 33.9 μmol/L; 95 % CI, 29.9-37.9; NO₂^-: 159.5 nmol/L; 95 % CI, 131.8-187.1; P < 0.01) and trained individuals (NO₃^-: 43.0 μmol/L; 95 % CI, 13.2-72.9; NO₂^-: 199.3 nmol/L; 95 % CI, 117.6-281; P < 0.01). Mean salivary NO₃^- and NO₂^- concentrations were 546.2 μmol/L and 197.8 μmol/L, respectively. Salivary NO₃^-, but no NO₂^-, 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 NO₃^- and diastolic blood pressure (DBP). These findings suggest that the health status is positively associated with plasma NO₃^- and NO₂^- concentrations, but the circulatory levels of these anions are not associated with blood pressure. Only salivary NO₃^- showed a significant positive association with DBP.