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.