Nitrate (NO3−) contained in food and beverages can transiently increase nitric oxide (NO) availability following a stepwise reduction to nitrite (NO2−) by commensal bacteria in the oral cavity. We tested the hypothesis that regular ingestion of dietary NO3− would influence the oral microbiome, the capacity to reduce NO3− to NO2− in saliva, and the vascular responses to an acute dose of NO3−. The abundance of bacterial species on the tongue, the availability of NO markers, and vascular function were assessed in 11 healthy males before and after 7 days of supplementation with NO3−-rich beetroot juice and a NO3−-depleted placebo. As expected, saliva and plasma NO2− and NO3− were significantly elevated after NO3− supplementation (all P < 0.05) but not placebo. We found that NO3− supplementation increased salivary pH (7.13 ± 0.54 to 7.39 ± 0.68, P = 0.043) and altered the abundance of some bacteria previously implicated in NO3− reduction: Neisseria (from 2% ± 3%–9% ± 5%, P < 0.001), Prevotella (from 34% ± 17%–23% ± 11%, P = 0.001) and Actinomyces (from 1% ± 1%–0.5% ± 0.4%). Despite these alterations to the oral microbiota, an acute dose of NO3− increased salivary and plasma NO2−, reduced systolic blood pressure and increased the response to flow mediated dilation to a similar extent before and after 7 days of supplementation (P > 0.05). Our study establishes that supplementing the diet with NO3− for a sustained period can alter the oral environment in favour of health but does not impact the response to an acute NO3− dose. Acute ingestion of NO3− results in transient improvements in vascular function but the dietary induced adaptations to the oral bacteria did not enhance these effects.
Burleigh, M., Liddle, L., Muggeridge, D. J., Monaghan, C., Sculthorpe, N., Butcher, J., Henriquez, F., & Easton, C. (2019). Dietary nitrate supplementation alters the oral microbiome but does not improve the vascular responses to an acute nitrate dose. Nitric Oxide, 89, 54-63. https://doi.org/10.1016/j.niox.2019.04.010