Ageing modifies the oral microbiome, nitric oxide bioavailability and vascular responses to dietary nitrate...

This study evaluated whether changes in the oral microbiome in response to dietary nitrate and antiseptic mouthwash treatments were related to changes in nitric oxide bioavailability and vascular function. Thirty-nine young (18-30 years) and thirty-six older (67-79 years) males and females completed a placebo-controlled, double-blind cross-over intervention including three 2-week conditions separated by 2-week washouts: placebo beetroot juice (PL), nitrate-rich beetroot juice (BR) and antiseptic mouthwash (MW). The oral microbiomes of young and older adults responded differently to BR (post BR non-metric multidimensional scaling P = 0.01), while the oral microbiomes of both age groups were unaffected by PL and MW interventions. Older people, who had elevated baseline mean arterial pressure (MAP; 95 ± 9 mmHg) compared to young adults (87 ± 7 mmHg, P < 0.001), showed decreased brachial MAP (-4±4 mmHg, P = 0.003) after BR while this effect was absent in the young. Flow mediated dilatation (FMD) variables were not affected by the interventions in older adults, while in the young there was a difference in changes (from pre to post) in ΔFMD% between the MW and BR conditions (P = 0.04). Decreased blood pressure in older adults correlated with increased plasma nitrite concentration (change in central MAP vs. [NO₂^-] r = -0.41, P = 0.02), which in turn correlated with decreases within the co-occurring module of bacteria dominated by the genus Prevotella (P. intermedia r = -0.72, P = 0.001; P. dentalis r = -0.88, P < 0.0001; Crassaminicella sp. SY095 r = -0.81, P < 0.0001). Greater blood pressure benefits from supplemental dietary nitrate in older compared to younger people are mediated primarily by the suppression of potentially harmful oral bacteria, that have been associated with ammonia production.