Nitrate causes a dose-dependent augmentation of nitric oxide status in healthy women
Green leafy vegetables, high in dietary nitrate, may contribute to cardiovascular health by augmenting nitric oxide status. The exogenous enterosalivary pathway of nitrate reduction to nitrite appears to be a critical determinant of the effects of nitrate. Our primary objective was to investigate the dose–response of nitrate intake on nitric oxide status and nitrate reduction in the mouth. We also assessed whether antibacterial toothpaste can inhibit nitrate reduction and blunt subsequent increases in circulating nitric oxide. A randomised, controlled, crossover trial with healthy women (n = 16) was conducted. The acute effects of four doses of nitrate (0 mg, 100 mg, 200 mg, 400 mg, as well as 400 mg plus antibacterial toothpaste), administered in random order, were compared. Measurements included biomarkers of plasma nitric oxide status, assessed by measuring S-nitrosothiols + other nitroso species (RXNO) and nitrite, and a biomarker of nitrate reduction in the mouth, assessed by measuring salivary nitrite. Compared to 0 mg, all doses of nitrate resulted in higher plasma RXNO and nitrite, and salivary nitrite (P < 0.05). A linear dose–response to nitrate intake was observed with plasma RXNO and nitrite, and salivary nitrite (P < 0.001). Antibacterial toothpaste did not alter nitrate reduction in the mouth (P > 0.9) or blunt the increase in nitric oxide status (P > 0.9). Thus, our study has demonstrated that increasing nitrate intake results in a dose-related increase in nitrate reduction in the mouth and nitric oxide status, and that use of antibacterial toothpaste does not inhibit nitrate reduction or blunt increases in circulating nitric oxide.