The main aim of the current study is to investigate whether consuming grapes rich in flavonoids just before mental stress can protect cerebrovascular and peripheral vascular function, mood and cognition, from the negative effects of mental stress in young healthy adults. A second, exploratory aim, will further address whether quality of habitual diet, microbiome health (composition; metabolites production e.g. Short-chain fatty acids) and levels of cardiorespiratory fitness play a role on the beneficial effects of grapes during mental stress. All participants will receive a high-flavonoid grape intervention (60 g freeze-dried grape powder, equivalent to 300 g fresh grapes) and a low-flavonoid grape intervention (60 g powdere isocaloric-matched control). It is hypothesized that the high-flavonoid grape intervention will improve cortical oxygenation and cognitive function in the context of mental stress, and prevent the stress-induced decline in peripheral endothelial function following stress. Furthermore, it is hypothesized that individuals with poorer diets, cardiorespiratory fitness and a poorer gut microbiome will benefit more from the grape intervention in the context of mental stress.
Males and females
18 - 40 years old
Smokers
Consumes > 21 units of alcohol per week
History of cardiovascular, respiratory, metabolic, liver or inflammatory diseases
Suffers from blood-clotting disorders
Crossover
High-flavonoid grape intervention
Dietary supplementHigh-flavonoid grape powder: 60 g, equivalent to 300 g fresh grapes. Total polyphenols: 437 mg/100g).
Low-flavonoid grape intervention
Dietary supplement60 g powder isocaloric-matched control (Total polyphenols: \< 60 mg)
Pre-frontal cortical Tissue Oxygenation Index (NIRS) - TOI
Pre-frontal levels of Tissue Oxygenation Index (% TOI) will be assessed by functional Near-Infrared Spectroscopy (fNIRS). The NIRS device measures changes in chromophore concentrations of oxyhaemoglobin (O2Hb) and deoxyhaemoglobin (HHb), providing depth-resolved measures of total tissue oxygen saturation.
Pre-frontal cortical Tissue Oxygenation Index (NIRS) - O2Hb
Pre-frontal levels of oxygenated (O2Hb) haemoglobin concentration (μmol) will be assessed by functional Near-Infrared Spectroscopy (fNIRS).
Pre-frontal cortical Tissue Oxygenation Index (NIRS) - HHb
Pre-frontal levels of deoxygenated (HHb) haemoglobin concentration (μmol) will be assessed by functional Near-Infrared Spectroscopy (fNIRS).
Pre-frontal cortical Tissue Oxygenation Index (NIRS) - nTHI
Pre-frontal levels of normalised haemoglobin index (relative value of total haemoglobin normalised to the initial value, nTHI) content (a.u.) will be assessed by functional Near-Infrared Spectroscopy (fNIRS).
Flow-mediated dilatation (FMD) of the brachial artery
FMD of the brachial artery. Expressed as % FMD: change in brachial diameter from baseline to peak dilation following 5 minutes of arterial occlusion. Brachial artery diameter and blood flow will be measured using Doppler ultrasonography (uSmart 3300, Terason).
Common Carotid Artery (CCA) - Blood flow
Common Carotid Artery (CCA) blood flow velocity (ml min-1) will be measured using Doppler ultrasonography (uSmart 3300, Terason) interfaced with the Quipu analysis software. CCA blood flow is calculated using CCA blood velocity and diameter across 2 minutes of recording.
Common Carotid Artery (CCA) - Shear rate
Common Carotid Artery (CCA) shear rate (s-1) will be measured using Doppler ultrasonography (uSmart 3300, Terason) interfaced with the Quipu analysis software.
Executive Function (MANT) - Accuracy
Executive function accuracy will be measured using the Modified Attention Network Task (MANT) which measures response to cognitive load
Forearm blood flow (FBF)
Venous occlusion plethysmography will assess the forearm vasodilatory response (ml/100ml/min) to mental stress.
Forearm vascular conductance (FVC)
Forearm vascular conductance (FVC) will be calculated by dividing FBF by beat-to-beat mean arterial pressure (MAP).
Cardiovascular activity - Heart rate (HR)
Heart rate (HR, bpm) is assessed using an electrocardiogram.
Cardiovascular activity - R-wave to pulse interval (RPI)
R-wave to pulse interval (RPI, ms) is assessed using an electrocardiogram, to provide an indication of sympathetic activity.
Click on the lead sponsor to view all of their trials.
University of Birmingham
Lead sponsor
California Table Grape Commission
Collaborator
