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.