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.
Clinically diagnosed Type 2 Diabetes Mellitus
Aged 40 to 65 years
Not treated with insulin
Stable diabetes medication regimen for at least 3 months
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
Crossover
Beetroot juice
Dietary supplementA 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.
Nitrate-depleted Beetroot Juice Placebo
Dietary supplementA 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.
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.
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.
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.
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.
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.
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.
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