Factors influencing the effects of dietary nitrate supplementation on nitric oxide biomarkers and blood pressure

Abstract

Ingestion of nitrate (NO3-) from natural sources can improve indices of cardiovascular health and exercise tolerance. The aim of this thesis was to determine the impact of dietary NO3- as a therapeutic aid when consumed amongst factors that might affect its efficacy such as antibacterial mouthwash, blood donation, different food forms and co-ingestion with alcoholic beverages. Young, healthy, normotensive individuals volunteered to participate in each experiment and undergo an array of physiological assessments. Chapter 4: Mouth rinsing with chlorhexidine and non-chlorhexidine mouthwash prior to consumption of concentrated NO3--rich beetroot juice (BR), over 6 days, blunted the rise in plasma nitrite concentration ([NO2-]) by 53 % and 29 % respectively, compared with control. Chlorhexidine mouthwash also elevated systolic (SBP) and mean arterial (MAP) blood pressure (BP) during treadmill walking. Chapter 5: Short-term BR ingestion lowered the oxygen (O2) cost of moderate-intensity exercise (by ~ 4 %), better preserved muscle oxygenation and attenuated the decline in incremental exercise tolerance (by 5 %) following whole blood donation. Chapter 6: An array of different NO3--rich vehicles, including BR, beetroot flapjack (BF), non-concentrated beetroot juice (BL) and beetroot crystals (BC), elevated salivary, plasma and urinary NO3- concentration ([NO3-]) and [NO2-] when compared with baseline and control, with the largest increases in plasma [NO2-] occurring in BF and BR. BR also reduced SBP (~5 mmHg) and MAP (~ 3-4 mmHg), and BF reduced diastolic BP (DBP; ~ 4 mmHg). Chapter 7: A high NO3- salad, accompanied by polyphenol-rich (NIT-RW) and -low (NIT-A) alcoholic beverages and a water control (NIT-CON) elevated salivary, plasma and urinary [NO3-] and [NO2-] compared with control (CON). SBP was reduced 2 h post consumption of NIT-RW (-4 mmHg), NIT-A (-3 mmHg) and NIT-CON (-2 mmHg) compared with CON. DBP and MAP were also lower in NIT-A, and more so in NIT-RW, compared with NIT-CON. Overall, the findings in this thesis demonstrate the efficacy of naturally derived NO3- on NO metabolites, BP and exercise tolerance. The potential for such benefits to arise may be maximised if antibacterial mouthwash is avoided during supplementation and if NO3- is consumed as BR, BF or as a green leafy salad with or without an alcoholic beverage. It may also be suggested that NO3- ingestion can offset decrements in exercise tolerance following blood donation.