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.