Oral Temperature and pH Influence Dietary Nitrate Metabolism in Healthy Adults

This study tested the hypothesis that the increases in salivary and plasma [NO(2)(−)] after dietary NO(3)(−) supplementation would be greater when oral temperature and pH were independently elevated, and increased further when oral temperature and pH were elevated concurrently. Seven healthy males (mean ± SD, age 23 ± 4 years) ingested 70 mL of beetroot juice concentrate (BR, which provided ~6.2 mmol NO(3)(−)) during six separate laboratory visits. In a randomised crossover experimental design, salivary and plasma [NO(3)(−)] and [NO(2)(−)] were assessed at a neutral oral pH with a low (T(Lo)-pH(Norm)), intermediate (T(Mid)-pH(Norm)), and high (T(Hi)-pH(Norm)) oral temperature, and when the oral pH was increased at a low (T(Lo)-pH(Hi)), intermediate (T(Mid)-pH(Hi)), and high (T(Hi)-pH(Hi)) oral temperature. Compared with the T(Mid)-pH(Norm) condition (976 ± 388 µM), the mean salivary [NO(2)(−)] 1–3 h post BR ingestion was higher in the T(Mid)-pH(Hi) (1855 ± 423 µM), T(Hi)-pH(Norm) (1371 ± 653 µM), T(Hi)-pH(Hi) (1792 ± 741 µM), T(Lo)-pH(Norm) (1495 ± 502 µM), and T(Lo)-pH(Hi) (2013 ± 662 µM) conditions, with salivary [NO(2)(−)] also higher at a given oral temperature when the oral pH was increased (p < 0.05). Plasma [NO(2)(−)] was higher 3 h post BR ingestion in the T(Mid)-pH(Hi), T(Hi)-pH(Hi), and T(Lo)-pH(Hi) conditions, but not the T(Lo)-pH(Norm) and T(Hi)-pH(Norm) conditions, compared with T(Mid)-pH(Norm) (p < 0.05). Therefore, despite ingesting the same NO(3)(−) dose, the increases in salivary [NO(2)(−)] varied depending on the temperature and pH of the oral cavity, while the plasma [NO(2)(−)] increased independently of oral temperature, but to a greater extent at a higher oral pH.