Inter-individual Variation in the Blood Pressure Lowering Effects of Dietary Nitrate

Overview

Dietary nitrate supplementation, often in the form of beetroot juice, has been shown to lower blood pressure and could play a role in preventing or treating hypertension. However, it is currently unclear: a) how reproducible this response is within the same individual on different occasions, and b) whether there are genuine individual differences in the blood pressure lowering effects of dietary nitrate. This study will use a novel replicated cross-over design (2 x nitrate conditions, 2 x placebo conditions) to examine the reproducibility and inter-individual variability in the blood pressure lowering effects of dietary nitrate supplementation.

The investigators will undertake a replicated cross-over randomised controlled trial (i.e., a study involving 2 x identical experimental conditions and 2 x identical control conditions), to explore the reproducibility of the blood pressure lowering effects of nitrate-rich beetroot juice, and to identify if there are genuine individual differences in the blood pressure-lowering effects of this supplement. Participants will be recruited via posters, email and social media, and interested individuals will be invited to attend the laboratory on 5 occasions. Visit 1: Potential participants will be invited to attend a screening session at Newcastle University to identify if they are eligible to participate. They will have an opportunity to discuss the study with a researcher and will provide written consent. They will then complete a screening questionnaire and provide a measure of their height, weight and blood pressure. Eligible participants will be invited to attend 4 experimental trials (2 x nitrate-rich beetroot juice conditions, 2 x placebo conditions) over 2-3 weeks with a minimum of 3 days wash-out between visits. If individuals are ineligible to participate this will be explained to them and they will be thanked for their time. Visits 2-5: On the day before the first trial, participants will be asked to record what they eat and then replicate this as closely as possible for all future visits. In the morning of each trial, participants will be asked to arrive at the laboratory between 7-9 am having fasted since 10 pm the night before. The participants will be required to rest for 10 minutes, after which a measure of their blood pressure will be obtained. Participants will then be provided with breakfast (a bowl of porridge) and 140 ml concentrated nitrate-rich (\~12.5 mmol nitrate) or nitrate-depleted beetroot juice (\~0 mmol nitrate). Participants will then be asked to sit in the laboratory for 2.5 hours, during which time they can read quietly or use a computer. The investigators will then obtain a further measure of their blood pressure and collect a blood sample from a vein in their arm via venepuncture, to measure markers of nitric oxide, a signalling molecule in the body which is thought to mediate the blood pressure lowering effects of nitrate-rich beetroot juice.