Modulation of the Gut-brain Axis by Cranberries: Impact on University Students' Mental Wellbeing

In this work, the investigators will assess whether cranberry (poly)phenols improve mood disorders including stress, anxiety and depression via the gut-brain axis in university students. The investigators will evaluate whether the effects observed are related to an improvement in gut microbiome diversity and function, and whether the mechanism of action may be mediated by a decrease in inflammatory markers, modulation of neurotransmitters or via an alteration of BDNF levels. The investigators will also quantify the most comprehensive panel of cranberry (poly)phenol metabolites. A double-blind, randomized placebo controlled 2-arm parallel study will be conducted in the Metabolic Research Unit (MRU, Department of Nutritional Sciences at KCL).

The study population will be final year BSc and MSc university students between 20-25 years old (n=60), who are generally healthy and not taking any medication. The study will be conducted during the period prior to their final exams (January until September). The intervention will be cranberry and placebo juice, consumed daily for 12 weeks, and will be provided free of cost by the Cranberry Institute. After a screening visit to evaluate inclusion and exclusion criteria, informed consent will be obtained, and subjects will be randomized to the treatments.

The study will consist in a total of 4 visits, one visit every 4 weeks over a total of 12 weeks intervention. Volunteers will consume a cranberry or a control drink every day for 12 weeks. The day before each visit (pre-visit), volunteers will self-collect a total of 6 saliva samples throughout the day to measure cortisol levels as a biomarker of stress. Mental health, cognitive function, diet and physical activity will also be assessed using self-reported questionnaires, an online cognitive battery test and an online 24 h dietary recall. In addition, on the day before visits 1 and 4 (baseline and 12 weeks), a stool sample will be self-collected to assess changes in gut microbiome diversity and composition. On the day of each visit, a spot urine sample will be self-collected after waking up and before breakfast. During each visit, volunteers will drop the self-collected samples, and will collect new kits for the next visit. Visits 1 and 4 will last approximately 20 min, while visits 2 and 3 will last approximately 5 minutes. In addition, during visits 1 and 4, blood samples will be taken to investigate changes in gut-brain axis and cranberry related metabolites. Blood samples will also be collected at baseline to assess general health status of participants (blood lipids, markers of liver and kidney function, urea, uric acid, creatinine, and glucose).

Eligibility Criteria:
Inclusion Criteria:

* Healthy men and women aged 20-25 years old.
* Final year BSc or MSc university students.
* Subjects are willing to maintain their normal eating/drinking habits and exercise habits to avoid changes in body weight over the duration of the study.
* Able to understand the nature of the study.
* Able and willing to give signed written informed consent.
* Comply with all study protocol procedures.

Exclusion Criteria:

* Subjects taking regular prescribed medication (including iron for anemia).
* Grade 1 hypertensive or above, as defined as SBP superior or equal to 140 mmHg or DBP superior or equal to 90 mmHg.
* Obese participants, defined as BMI superior or equal to 30.
* Diabetes mellitus and metabolic syndrome.
* Chronic and acute disease.
* Terminal renal failure and other kidney abnormalities.
* Malignancies.
* Allergies to berries or other significant food allergy.
* Subjects who took food supplements, dietary supplement or herbal remedies within 1 month of study start.
* Subjects who have lost more than 10% of their weight in the past 6 months or are currently in a diet.
* Subjects with allergies to berries or other relevant/related food.
* Subjects who reported participant in another study within one month before the study start.
* Subjects who smoke an irregular number of cigarettes per day or plan quitting smoking in the next 3 months.
* Subjects who require chronic antimicrobial or antiviral treatment
* Subjects with unstable psychological condition (diagnosed with mental health disorders).
* Subjects with history of cancer, myocardial infarction, cerebrovascular incident
* Pregnant, lactating or planning to become pregnant, as well as pre-menopausal women who do not have a regular menstrual cycle and do not adequate method of contraception.
* Any reason or condition that in the judgement of the clinical investigator(s) may put the subject at unacceptable risk or that may preclude the subject from understanding or complying with the study's requirements.