Abstract/Summary

Inorganic (dietary) nitrate, found mainly in green leafy vegetables and beetroot has been repeatedly demonstrated to reduce blood pressure (BP) and induce other vascular benefits by increasing nitric oxide (NO), an established vasodilator via the exogenous nitrate-nitrite- NO pathway. While most research has focused on the impact on BP, other aspects of vascular function are less researched, including macro and microvascular function and subsequent effects on cognition. It is possible that vascular improvements could translate to improved cerebral blood flow and, consequently, improved cognition. A systematic review with meta-analysis of randomised controlled trials was undertaken (Chapter 2) to determine how endothelial function, measured by means of flow-mediated dilation (FMD), is impacted by inorganic nitrate consumption. Thirteen studies were included in the review and revealed that the consumption of inorganic nitrate was associated with a 1.45% improvement in FMD response. Chapter 3 involved assessing the impact of inorganic nitrate-rich beetroot juice (BJ, 400 mg) on microvascular and cognitive function in postmenopausal women in a randomised controlled trial. The potential impact of betalains, present in beetroot, was also evaluated by adding another arm with potassium nitrate added to control juice (KNO3, 400mg). Participants were given either BJ, control juice or KNO3. This trial demonstrated that the acute consumption of inorganic nitrate drinks improved endothelium-independent microvascular reactivity (KNO3, p= 0.005; beetroot juice, p= 0.002). Furthermore, intervention drinks improved episodic memory outcomes, which were associated with short- and long-term memory assessment, concluding that microvascular reactivity might improve cerebral blood flow and, eventually, cognition. The final part of the thesis (Chapter 4), we assessed commercially available beetroot-based products: powders (n= 19); pills (n= 28); and drinks (n= 8) by ozone chemiluminescence. There is an increasing demand for these products due to their health benefits. Additionally, there is a concern about levels of nitrate consumed due to possible carcinogenicity. We found that the total nitrate amount in products ranged from 2 to 646 mg (per serving), while the coefficient of variation of three samples of the same product ranged from 1-72%. Results underscore the significance of selecting nitrate supplements selection to obtain a health benefits and ensure safe nitrate intake. Overall, this thesis demonstrates the potential for inorganic nitrate to be an important tool to protect from vascular disease and cognitive decline.