Effect of Beetroot Juice on Cardiovascular and Autonomic Responses to Exercise in Adults With Type 2 Diabetes (DiaBEET)

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.