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NCT Number: NCT06923722

De-stressing the Brain: Can Eating Grapes During Periods of Mental Stress Protect Brain and Vascular Health in Young Adults

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.

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Key information

Conditions

Healthy Behavior Behavioral Symptoms Stress, Psychological

Age range

18 year–40 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

School of Sport, Exercise & Rehabilitation Sciences

Birmingham, West Midlands, B15 2TT, United Kingdom

Location status: Recruiting

Location contact

Catarina Rendeiro

CONTACT

[email protected]

+44 7389190669

About this study

Psychological stress is widespread in our societies, and has been extensively shown to have negative consequences for human health. Specifically, psychological stress induces significant declines in human vascular function, as measured by brachial Flow-mediated Dilatation (FMD). We have demonstrated that flavonoid interventions can prevent the harmful effects of stress on the vascular system. Indeed, flavonoid-rich interventions have also been extensively shown to improve peripheral and cerebrovascular function in the absence of stress. However, the effect of flavonoids on cerebrovascular function and cognition in the context of mental stress is unknown. In the proposed project, our key objectives are to investigate whether grape intake prior to a mental stress task results in better brain oxygenation and vascular function, which leads to improved cognitive performance and mood in young healthy adults. These data will establish whether grapes can be effective as a 'stress snack' to optimize cognitive and brain function in the context of psychological stress. Furthermore, we will explore whether there are certain participant characteristics that mediate the impact of grape flavonoids on cerebrovascular function and cognition in the context of mental stress. Such as, physical fitness (assessed by a VO2 max test), composition of gut microbiome (assessed by faecal sample), habitual diet (assessed by 3-day food diary and the food frequency questionnaire), and eating behaviour and chronic stress (assessed by the eating behaviour questionnaire and perceived stress scale). This work will be important to guide future dietary recommendations around stress and might ultimately result in increased intake of flavonoid-rich grapes and other flavonoid-rich fruits/vegetables overall.

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Males and females
  • 18 - 40 years old

Exclusion criteria

  • Smokers
  • Consumes > 21 units of alcohol per week
  • History of cardiovascular, respiratory, metabolic, liver or inflammatory diseases
  • Suffers from blood-clotting disorders
  • Allergies or intolerances to foods
  • On a weight reducing dietary regiment
  • Currently taking dietary supplements, including fatty acids and vitamins
  • On long-term medication or have been on antibiotics in the last 3 months
  • Has an infection at present (e.g. cold) or viral infection

Treatment and study plan

High-flavonoid grape intervention

Dietary Supplement

High-flavonoid grape powder: 60 g, equivalent to 300 g fresh grapes. Total polyphenols: 437 mg/100g).

Low-flavonoid grape intervention

Dietary Supplement

60 g powder isocaloric-matched control (Total polyphenols: < 60 mg)

Primary outcomes

  1. Pre-frontal cortical Tissue Oxygenation Index (NIRS) - TOI

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during mental stress) and 1 hour 15 minutes post-intervention (during cognitive tasks, 10 minutes post-stress)

    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.

  2. Pre-frontal cortical Tissue Oxygenation Index (NIRS) - O2Hb

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during mental stress) and 1 hour 15 minutes post-intervention (during cognitive tasks, 10 minutes post-stress).

    Pre-frontal levels of oxygenated (O2Hb) haemoglobin concentration (μmol) will be assessed by functional Near-Infrared Spectroscopy (fNIRS).

  3. Pre-frontal cortical Tissue Oxygenation Index (NIRS) - HHb

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during mental stress) and 1 hour 15 minutes post-intervention (during cognitive tasks, 10 minutes post-stress).

    Pre-frontal levels of deoxygenated (HHb) haemoglobin concentration (μmol) will be assessed by functional Near-Infrared Spectroscopy (fNIRS).

  4. Pre-frontal cortical Tissue Oxygenation Index (NIRS) - nTHI

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during mental stress) and 1 hour 15 minutes post-intervention (during cognitive tasks, 10 minutes post-stress).

    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).

Secondary outcomes

  1. Flow-mediated dilatation (FMD) of the brachial artery

    Time frame: Change from pre-intervention baseline to 2 hours and 2 hours 45 minutes post-intervention (45-90 minutes post-stress).

    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).

  2. Common Carotid Artery (CCA) - Blood flow

    Time frame: Change from pre-intervention baseline to 2 hours and 2 hours 45 minutes post-intervention (45-90 minutes post-stress).

    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.

  3. Common Carotid Artery (CCA) - Shear rate

    Time frame: Change from pre-intervention baseline to 2 hours and 2 hours 45 minutes post-intervention (45-90 minutes post-stress).

    Common Carotid Artery (CCA) shear rate (s-1) will be measured using Doppler ultrasonography (uSmart 3300, Terason) interfaced with the Quipu analysis software.

  4. Executive Function (MANT) - Accuracy

    Time frame: Change from pre-intervention baseline to 1 hour 15 minutes post-intervention (10 minutes post-stress).

    Executive function accuracy will be measured using the Modified Attention Network Task (MANT) which measures response to cognitive load

  5. Executive Function (Switch) - Accuracy

    Time frame: Change from pre-intervention baseline to 1 hour 15 minutes post-intervention (10 minutes post-stress).

    Executive function accuracy will be measured using the Switch Task which considers cognitive flexibility.

  6. Executive Function (MANT) - Reaction time

    Time frame: Change from pre-intervention baseline to 1 hour 15 minutes post-intervention (10 minutes post-stress).

    Executive function reaction time will be measured using Modified Attention Network Task (MANT) which measures response to cognitive load.

  7. Executive Function (Switch) - Reaction time

    Time frame: Change from pre-intervention baseline to 1 hour 15 minutes post-intervention (10 minutes post-stress).

    Executive function reaction time will be measured using the Switch Task which considers cognitive flexibility.

  8. Executive Function (MANT) - Inverse Efficiency Score

    Time frame: Change from pre-intervention baseline to 1 hour 15 minutes post-intervention (10 minutes post-stress).

    Executive function inverse efficiency will be measured using the Modified Attention Network Task (MANT), calculated by dividing task reaction time by task accuracy.

  9. Executive Function (Switch) - Inverse Efficiency Score

    Time frame: Change from pre-intervention baseline to 1 hour 15 minutes post-intervention (10 minutes post-stress).

    Executive function inverse efficiency will be measured using the Switch Task, calculated by dividing task reaction time by task accuracy.

  10. Mood (POMS)

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (immediately following stress), 2 hours and 2 hours 45 minutes post-intervention (45-90 minutes post-stress).

    Mood (total mood disturbance, TMD) will be assessed by the questionnaire Profile-of-Mood-States (POMS).

Other outcomes

  1. Forearm blood flow (FBF)

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during 8 minutes rest and 8 minutes of mental stress).

    Venous occlusion plethysmography will assess the forearm vasodilatory response (ml/100ml/min) to mental stress.

  2. Forearm vascular conductance (FVC)

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during 8 minutes rest and 8 minutes of mental stress).

    Forearm vascular conductance (FVC) will be calculated by dividing FBF by beat-to-beat mean arterial pressure (MAP).

  3. Cardiovascular activity - Heart rate (HR)

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during 8 minutes rest and 8 minutes of mental stress).

    Heart rate (HR, bpm) is assessed using an electrocardiogram.

  4. Cardiovascular activity - R-wave to pulse interval (RPI)

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during 8 minutes rest and 8 minutes of mental stress).

    R-wave to pulse interval (RPI, ms) is assessed using an electrocardiogram, to provide an indication of sympathetic activity.

  5. Cardiovascular activity - Heart rate variability (HRV)

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during 8 minutes rest and 8 minutes of mental stress).

    Heart rate variability (HRV, ms) is assessed using an electrocardiogram, to provide an indication of parasympathetic activity.

  6. Cardiovascular activity - beat-to-beat systolic blood pressure (SBP)

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during 8 minutes rest and 8 minutes of mental stress).

    Beat-to-beat systolic blood pressure (SBP) will be measured using a Finometer (mmHg).

  7. Cardiovascular activity - beat-to-beat diastolic blood pressure (DBP)

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during 8 minutes rest and 8 minutes of mental stress).

    Beat-to-beat diastolic blood pressure (SBP) will be measured using a Finometer (mmHg).

  8. Cardiovascular activity - beat-to-beat mean arterial pressure (MAP)

    Time frame: Change from pre-intervention baseline to 1 hour post-intervention (during 8 minutes rest and 8 minutes of mental stress).

    Beat-to-beat mean arterial pressure (MAP) will be measured using a Finometer (mmHg).

  9. Brachial Systolic Blood Pressure (SBP)

    Time frame: Change from pre-intervention baseline to 1 hour 15 minutes post-intervention (10 minutes post-stress), 2 hours post-intervention (45 minutes post-stress) and 2 hour 45 minutes post-intervention (90 minutes post-stress).

    Resting systolic blood pressure (mmHg) will be measured using an automated oscillometric blood pressure monitor, with a cuff attached to the right upper arm, following at least 10 minutes rest.

  10. Brachial Diastolic Blood Pressure (DBP)

    Time frame: Change from pre-intervention baseline to 1 hour 15 minutes post-intervention (10 minutes post-stress), 2 hours post-intervention (45 minutes post-stress) and 2 hour 45 minutes post-intervention (90 minutes post-stress).

    Resting diastolic blood pressure (mmHg) will be measured using an automated oscillometric blood pressure monitor, with a cuff attached to the right upper arm, following at least 10 minutes rest.

Sponsors and collaborators

Lead sponsor

University of Birmingham

Other

Collaborators

  • California Table Grape Commission

Registry information

Official study title

A Placebo-controlled, Randomized, Double-masked, Cross-over Acute Intervention Study Investigating the Effects of Grape Polyphenols on Cerebral Oxygenation, Cognitive and Vascular Function in the Context of Mental Stress in Young Adults

Important dates

Study start
2025
Primary completion
2026
Study completion
2026
First posted
Apr 11, 2025
Registry last updated
Dec 4, 2025

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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