Lowering salivary pH with sugar‐containing gum augments salivary nitrite production and blood pressure reduction with dietary nitrate (beetroot juice)
Andrew J. Webb, Harriet Clift, Callum Hill, Nur Mousa, Navanithan Arun Jayaraj, Jasmine Quraishi, Charlotte E. Mills, Kevin O'GallagherAims
The nitrate–nitrite–nitric oxide (NO) pathway has a wide range of effects including blood pressure (BP) regulation. Nitrate, produced endogenously, and absorbed from dietary sources (e.g., beetroot), is concentrated in/secreted by the salivary glands and reduced by lingual bacterial nitrate reductases to nitrite (the ‘enterosalivary circulation’). Following systemic absorption, nitrite is further reduced to vasodilating NO intravascularly. The role of salivary pH in nitrate reduction has mainly been studied in isolated oral installation studies, rather than systemic studies employing the enterosalivary circulation. Our aim was to determine the acute relationship between salivary pH, salivary nitrite production, plasma [nitrite] and the BP‐lowering effect of dietary nitrate, by altering salivary pH using sugar‐containing chewing gum ( vs . sugar‐free chewing gum).
Methods
We performed a 7‐h crossover study, with 14 healthy volunteers consuming beetroot juice (Beet‐It®, 70‐mL, ~400‐mg nitrate) and randomized to initially chew either sugar‐containing acidic chewing (bubble) gum or sugar‐free non‐acidic chewing gum, with the alternate gum on the second visit.
Results
Sugar‐containing gum decreased salivary pH by 1.4 ± 0.09 vs . sugar‐free gum ( p < .0001). While there was no significant effect on salivary nitrate secretion or plasma [nitrate], salivary nitrite production was increased by 45% (30.0 ± 11.0 μmol·h −1 ; [ p < .01]), with plasma [nitrite] increasing by 25% (222.2 ± 50.3 nmol·L −1 ; [ p = .0001]). Systolic and diastolic BP were decreased by 2.7 ± 0.5 and 1.9 ± 0.5 mmHg, respectively (both p < .0001).
Conclusion
Acutely lowering salivary pH (with sugar‐containing gum) augments salivary nitrite production, plasma [nitrite] and BP‐lowering with dietary nitrate. This mechanism has potential to enhance other nitrate–nitrite–NO pathway effects, for example, exercise performance.