Dietary nitrate supplementation alters the oral microbiome but does not improve the vascular responses to an acute nitrate dose

Abstract

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.