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.

Inclusion Criteria:

• Clinically diagnosed Type 2 Diabetes Mellitus
• Aged 40 to 65 years
• Not treated with insulin
• Stable diabetes medication regimen for at least 3 months
• Able to understand the study information and provide informed consent
• Able to safely perform light-to-moderate cycling exercise

Exclusion Criteria:

• Current or recent use of insulin
• Use of organic nitrates (e.g., glyceryl trinitrate) or phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil)
• Use of systemic antibiotics within the specified preparation period or regular use of antiseptic/antibacterial mouthwash during study participation
• Use of supplements known to interfere with nitric oxide metabolism within the defined preparation period
• Unstable or clinically significant cardiovascular disease
• Uncontrolled hypertension or any condition that makes exercise unsafe
• Chronic kidney disease, history of kidney stones, or other relevant renal conditions
• Neurological, musculoskeletal or systemic disorders that impair safe participation
• Known or suspected allergy or intolerance to beetroot, lemon or any component of the study products
• Pregnancy or breastfeeding
• Inability to comply with study preparation requirements

The de-identified IPD used in the results publication will be made available on the Oxford Brookes University Research And Digital Assets Repository (RADAR)

At the time of submission for journal publication of results

RADAR shares the intellectual product of Oxford Brookes University freely and openly, either with the staff and students of Oxford Brookes or with the general public and global academic community.

An independent laboratory technician, not involved in data collection or analysis, is responsible for generating the randomization sequence and preparing and labeling the study drinks using participant ID codes. This individual is the only unblinded member of the study team. The intervention and placebo are matched for appearance, taste and packaging to maintain blinding throughout the study.