Anti-bacterial mouthwash reduces plasma nitrite following dietary nitrate supplementation but does not alter stress response

Rinsing the mouth with anti-bacterial mouthwash (MW) suppresses the reduction of nitrate (NO3 -) to nitrite (NO2 -) and nullifies the reduction in blood pressure (BP) often reported after dietary NO3 - supplementation. Given the known interactions between the microbiome and the central nervous system, we speculated that disruption of the oral flora with MW would induce a stress response exemplified by increased BP and cortisol secretion. PURPOSE: To determine the effects of ingesting NO3 --rich beetroot juice (BR) and using MW on BP, plasma [NO2 -] and [NO3 -], and salivary [cortisol]. METHODS: After a ‘no treatment’ control (CON), ten healthy male participants rinsed with an inert placebo mouthwash (PM) prior to ingestion of 5 x 70 ml BR (~31 mmol NO3 -) over the 24 h prior to the experiment (PM+BR) followed by two further experimental arms conducted in a randomised order. In one arm, participants used MW prior to ingestion of BR (MW+BR) and in the other they used MW prior to the ingestion of a NO3 --depleted beetroot juice placebo (MW+PLA). Blood was collected and measurements performed after 30 min of laying supine. Plasma [NO2 -] and [NO3 -] were measured by chemiluminescence. RESULTS: Plasma [NO2 -] in PM+BR (209 ± 98 nM) was elevated in comparison to all other experimental arms (all P<0.04). Plasma [NO2 -] was similar between CON (95 ± 27 nM) and MW+BR (115 ± 57 nM, P=1.0) but lower in MW+PLA (41 ± 24 nM) compared to all other arms (all P<0.03). Plasma [NO3 -] was higher in PM+BR (382 ± 104 μM) and MW+BR (412 ± 87 μM) both compared separately to CON and MW+PLA (all P<0.001). Plasma [NO3 -] was not different between CON (64 ± 24 μM) and MW+PLA (43 ± 14 μM, P=0.385) or between PM+BR and MW+BR (P=1.0). Diastolic BP was lower in PM+BR (63 ± 5 mmHg) compared to MW+BR (67 ± 5 mmHg, P=0.018) but not different between other experimental arms (all P>0.43). There were no differences in systolic BP, mean arterial BP, or salivary cortisol between any arms of the experiment (all P>0.16). CONCLUSIONS: As expected, MW reduced plasma [NO2 -] but not [NO3 -], with and without ingestion of BR. Contrary to our hypothesis, however, MW did not alter BP or cortisol levels suggesting that it does not induce a stress response with short-term use. Further research employing a longer intervention and more extensive assessment of stress markers is required to confirm these observations.