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

Abstract

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 mu mol/L and 158.3 nmol/L, respectively. Subgroup analyses revealed lower plasma NO3- and NO2- concentrations in individuals with cardiometabolic risk (NO3-: 21.2 mu mol/L; 95 % CI, 13.4-29.0; NO2-: 122.8 nmol/L; 95 % CI, 75.3-138.9) compared to healthy (NO3-: 33.9 mu mol/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 mu mol/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 mu mol/L and 197.8 mu mol/L, respectively. Salivary NO3-, but no NO2-, concentrations were higher in individuals with cardiometabolic risk (680.0 mu mol/L; 95 % CI, 510.2-849.8; P = 0.001) compared to healthy individuals (535.9 mu mol/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.