This study will investigate whether a single dose of beetroot juice can improve cardiovascular responses and recovery after exercise in adults with Type 2 Diabetes. Type 2 Diabetes is associated with higher blood pressure, impaired blood vessel function, and reduced autonomic control of the heart, all of which increase cardiovascular risk and may affect how the body responds to and recovers from physical activity. Beetroot juice is naturally rich in dietary nitrate, which is converted in the body into nitric oxide, a molecule that helps blood vessels relax and improve blood flow. While these effects have been demonstrated in healthy individuals, less is known about their impact in people with Type 2 Diabetes. In this study, approximately 16 to 20 adults aged 40 to 65 years with Type 2 Diabetes will take part. After an online screening and consent process, eligible participants will attend two laboratory visits at Oxford Brookes University. In a randomised, double-blind, placebo-controlled crossover design, participants will receive beetroot juice during one visit and a nitrate-depleted placebo during the other visit. During each visit, participants will undergo physiological measurements, including blood pressure, heart rate, oxygen saturation, and capillary blood glucose. Participants will then complete a short session of supervised, light-to-moderate cycling exercise. Measurements will continue during the recovery period to assess how quickly the cardiovascular system returns to resting levels. The main outcomes are systolic blood pressure and heart rate variability during recovery, which reflect cardiovascular regulation and autonomic function. Secondary outcomes include diastolic blood pressure, heart rate, blood glucose, and markers related to nitric oxide availability. This study may help determine whether a simple, dietary-based intervention such as beetroot juice can support cardiovascular function and improve recovery after exercise in people living with Type 2 Diabetes.
Type 2 diabetes mellitus (T2DM) is characterised by endothelial dysfunction, elevated blood pressure and impaired autonomic regulation, all of which contribute to increased cardiovascular risk. In particular, reduced cardiovagal modulation and delayed recovery of cardiovascular parameters following exercise are associated with adverse clinical outcomes. These disturbances are closely linked to reduced nitric oxide bioavailability. Dietary inorganic nitrate, abundant in beetroot juice, is converted via the entero-salivary nitrate-nitrite-nitric oxide pathway into nitric oxide, promoting vasodilation, improved endothelial function and reductions in blood pressure. Acute supplementation with nitrate-rich beetroot juice has been shown to enhance nitric oxide bioavailability within approximately 2 to 3 hours after ingestion, making it suitable for investigating short-term physiological responses. However, evidence in individuals with T2DM remains limited, particularly regarding post-exercise autonomic recovery. This study is designed as a randomised, double-blind, placebo-controlled crossover trial to evaluate the acute effects of nitrate-rich beetroot juice on cardiovascular and autonomic responses to exercise in adults with T2DM not treated with insulin. Each participant will complete two experimental conditions, receiving nitrate-rich beetroot juice and a nitrate-depleted placebo in random order, separated by an adequate washout period. Randomisation will be performed using a computer-generated sequence by an independent researcher, and both participants and investigators will remain blinded to allocation. All procedures will be conducted in a controlled laboratory environment under supervision by trained research staff. Continuous physiological monitoring will be performed to capture cardiovascular responses at rest, during exercise and throughout the recovery period. The exercise protocol consists of a standardised, light-to-moderate intensity cycling task designed to provide a consistent physiological stimulus while minimising risk. The primary focus of the study is on post-exercise recovery, with particular emphasis on heart rate variability as an index of autonomic (vagal) modulation and systolic blood pressure as a marker of haemodynamic regulation. The crossover design allows each participant to serve as their own control, improving statistical efficiency and reducing inter-individual variability. Safety procedures are integrated throughout the protocol, including pre-participation screening, standardised preparation requirements and continuous monitoring during all experimental phases. The study is conducted as a low-risk laboratory protocol, with predefined procedures for the management of any adverse or unexpected physiological responses. The findings of this study are expected to contribute to the understanding of whether acute dietary nitrate supplementation can improve cardiovascular regulation and autonomic recovery following exercise in individuals with T2DM, providing mechanistic insight and potential implications for non-pharmacological strategies to support cardiovascular health in this population.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
TRIPLE
Enrollment
20
A single dose of approximately 70 mL of nitrate-rich beetroot juice providing approximately 400 mg of inorganic nitrate will be administered. The product consists of concentrated beetroot juice with a small amount of lemon juice and is consumed prior to exercise testing. The timing of ingestion is standardized to allow peak nitrate-nitrite-nitric oxide conversion within approximately 2 to 3 hours. This intervention is intended to increase nitric oxide bioavailability and assess its acute effects on cardiovascular and autonomic responses.
A nitrate-depleted beetroot juice placebo matched for appearance, taste and packaging will be administered in a single dose of approximately 70 mL. The placebo is identical to the active intervention in all aspects except for nitrate content. It is consumed under the same standardized conditions and timing as the active intervention to maintain blinding and allow controlled comparison of physiological responses.
Clinical Physiology Laboratory, Oxford Brookes University
Oxford, Oxfordshire, United Kingdom
Systolic Blood Pressure During Post-Exercise Recovery
Systolic blood pressure will be measured continuously during the post-exercise recovery period following submaximal cycling using beat-to-beat monitoring. This measure will be used to assess haemodynamic regulation after exercise under each intervention condition.
Time frame: During post-exercise recovery mean value at 0-10 minutes, 10-20 minutes, 20-30 minutes, and 50-60 minutes.
Heart Rate Variability (RMSSD) During Post-Exercise Recovery
Heart rate variability, expressed as the root mean square of successive differences (RMSSD), will be derived from continuous electrocardiogram recordings during the post-exercise recovery period following submaximal cycling. This measure will be used to assess autonomic (vagal) recovery after exercise under each intervention condition.
Time frame: During post-exercise recovery at 0-10 minutes, 10-20 minutes, 20-30 minutes, and 50-60 minutes.
Diastolic Blood Pressure During Post-Exercise Recovery
Diastolic blood pressure will be measured continuously during the post-exercise recovery period following submaximal cycling using beat-to-beat monitoring. This measure will be used to assess haemodynamic responses and vascular regulation after exercise under each intervention condition.
Time frame: During post-exercise recovery mean value at 0-10 minutes, 10-20 minutes, 20-30 minutes, and 50-60 minutes.
Heart Rate During Post-Exercise and Recovery
Heart rate will be measured continuously during submaximal cycling exercise and throughout the post-exercise recovery period using electrocardiogram monitoring. This measure will be used to assess cardiovascular response to exercise and the rate of recovery toward resting levels under each intervention condition.
Time frame: During post-exercise recovery mean value at 0-10 minutes, 10-20 minutes, 20-30 minutes, and 50-60 minutes.
Capillary Blood Glucose Response
Capillary blood glucose will be measured using finger-prick sampling at predefined time points, including pre-ingestion, 15, 30, 45, 60, 90 and 120 minutes post-ingestion, and at 5 and 60 minutes post-exercise. These measurements will be used to assess glycaemic response to the intervention and exercise under each experimental condition.
Time frame: Pre-ingestion; 15, 30, 45, 60, 90, and 120 minutes post-ingestion; and 5 and 60 minutes post-exercise
Salivary Nitric Oxide-Related Response
Salivary nitric oxide-related response will be assessed using test strips that estimate nitrate and nitrite concentrations in saliva. Measurements will be performed at baseline, 1 hour post-ingestion, and 2 hours post-ingestion. This measure will be used as an indicator of nitric oxide bioavailability following dietary nitrate supplementation under each experimental condition.
Time frame: Baseline, 1 hour post-ingestion, and 2 hours post-ingestion.
Perceived Exertion During Exercise
Perceived exertion will be assessed during the submaximal cycling ramp test using the Borg Rating of Perceived Exertion (6-20 scale). The scale ranges from 6 (no exertion) to 20 (maximal exertion), with higher scores indicating greater perceived effort. Ratings will be collected every minute during the exercise test and at peak exercise under each intervention condition.
Time frame: On both test days (beetroot juice and placebo days) perceived exertion will be recorded every minute during the submaximal cycling ramp test from timepoint M3 (2 hours post-ingestion) to timepoint M4 (peak exercise)
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