Effect of beetroot juice on blood pressure in unmedicated adults with high blood pressure

The Intervention is nitrate-rich beetroot juice. This study is an acute dose-response, crossover, double-blinded, randomised, placebo-controlled trial (RCT). Materials: Nitrate-Rich Beetroot Juice: The beetroot juice was prepared at the FoodBowl in Auckland, New Zealand. The concentrated beetroot juice drink, which includes natural flavours and contains no added sweeteners or preservatives, is pasteurised at 90°C for 5 seconds and then filled into Polyethylene Terephthalate (PET) bottles under aseptic conditions. The drinks are stored at -20°C until use and tested for microbial safety. Quality Control: Drinks are stored at -20°C. Thawing will be done at 4°C before administration, and disposed of if not used on the trial day. Placebo Drink: Similar in appearance and taste to beetroot juice but with minimal nitrate content. Each drink contains varying nitrate concentrations: * Placebo: less than 62 mg (1 mmol) * Low Dose: 400 mg (6.45 mmol) nitrate. * Medium Dose: 600 mg (9.68 mmol) nitrate. * High Dose: 800 mg (12.9 mmol) nitrate. Health Screening Questionnaire: Used to assess participants' eligibility. Blood Pressure Monitor: Riester Ri-champion 'Registered Trademark' N monitor. Ultrasonographic Cardiac Output Measurement Device: For haemodynamic measurements. Two-Day Food Diary: To record dietary intake before trial visits. Informed Consent Forms: Detailed participant information and consent documentation. These materials are provided to participants during the study visits and can be accessed through the study team at Massey University. Procedures: Screening Visits: The study consists of two health screenings and familiarisation sessions to confirm the eligibility of participants. Trial Visits: The study consists of four trial visits. Each participant will consume all four nitrate concentrations across separate visits, with one specific concentration consumed per visit. The order of the concentrations will be randomised for each participant. At the end of the first trial visit, the participant will be asked to visit for the next trial date (second) after at least a 7-day washout period. On the subsequent trial visits, these steps will be repeated with the remaining beetroot juice doses. Participants will complete pre-supplementation (baseline) measures, and then will be provided a randomly assigned (double blind) beetroot juice. Dosage: Participants consume a single shot of 100 ml of beetroot juice within 10 minutes. Administration: Participants consume the randomly assigned drink on-site with a standardised breakfast. A waiting time for 2.5-3.5 hours (the time it takes for the plasma nitrate and nitrite levels to peak) will be followed, and then post-supplementation measures will be taken. * The standardised isocaloric breakfast consists either cereal with milk or toast with peanut butter, designed to provide a balanced macronutrient intake of approximately 15 grams of protein, 30 grams of carbohydrates, and 10 grams of fat; this meal will be consumed alongside 100 ml of one of four different nitrate dosages of beetroot juice. * The total duration of each trial visit is approximately 4 hours. The pre-supplementation (baseline) assessment comprises measures that will be repeated post-supplementation, including: * Data Collection: Recording of blood pressure and haemodynamic measurements (heart rate, stroke volume, cardiac output, and systemic vascular resistance). * Blood Sample Collection: For plasma nitrate and nitrite analysis, serving as biomarkers for nitric oxide bioavailability Personalisation: The intervention is not personalised or titrated. All participants receive the same four doses of BRJ in a randomised order. Intervention Providers: * Co-ordinating Investigator: Prof Ajmol Ali, expertise in sport and exercise science. * PhD Candidate: Reder Mohammedsalih (10+ years academic experience, nutritionist registered in NZ, Medically Laboratory Registered (MLT) in NZ, certified in Comprehensive First Aid), responsible for day-to-day study management. * Study Management Group: Experienced researchers and academic staff from Massey University. * Medically Qualified Clinician: Dr. Sadiq Al-Sakini, MBChB, MSc, FRCPA, MCNZ Registration Number: 23030. Dr. Al-Sakini will review blood pressure results, medical history, and other relevant data to ensure participant safety. Location: The study will be conducted at the Sport and Exercise Science Research Laboratory, School of Sport, Exercise and Nutrition, Massey University, Auckland. The facility is equipped with the necessary infrastructure for conducting clinical trials, including private rooms for health screenings and laboratory space for trial visits. Adherence and fidelity will be assessed through direct observation by the research team and participant self-reports. Participants will be monitored during each visit to ensure they follow the study protocols, including the consumption of the assigned beetroot juice dose and adherence to pre-visit instructions (e.g., fasting, avoiding certain foods). Additionally, participants will have the opportunity to contact the researcher to provide feedback and report any issues. The research team, including the Co-ordinating Investigator, PhD candidate, study management group, and medically qualified clinician, will be responsible for assessing adherence and fidelity. To maintain or improve fidelity, several strategies will be employed. Participants will receive reminders about study protocols and the importance of adherence during each visit. All procedures, including the preparation and administration of the beetroot juice, will follow standardised protocols to ensure consistency. During the pre-assessment baseline, participants with blood pressure outside the predefined range (120-159/80-99 mmHg) at screening or subsequent visits will be withdrawn, considering pre- and post-supplementation readings and the rate of blood pressure change. The clinician will review blood pressure results, medical history, and other relevant data to ensure participant safety during the screening process and throughout the study.