Effects of Hydroxytyrosol-Rich Olive Polyphenol Dietary Supplement Combined With Mediterranean Diet Adherence on the Cognitive Health of Patients With Mild Cognitive Impairment

Inclusion Criteria: * GR-based men and women aged 50 - 85 * Willingness and ability to conform to the full protocol. * Ability to accept and sign the consent form. * Presence of a diagnostic classification of Mild Cognitive Impairment according to the National Institute on Aging and Alzheimer's Association (NIA-AA) framework MCI, which corresponds to stage 3 on the pre-dementia range. * MoCA score of ≥18 and ≤ 26. Or * MMSE (Mini-Mental State Examination) score of ≥26 and ≤ 28. * No active suicide ideation based on the Columbia-Suicide Severity Rating Scale. * Absence of severe depressive symptomatology based on the Geriatric Depression Scale-15. * Not using any laxative drugs for at least three days prior to the screening visit. * Information about APOE status Exclusion Criteria: * Patients with mild, moderate, or severe dementia. * Current or recent (within the last 4 weeks) engagement with a strict dietary regime i.e., vegetarian / vegan / ketogenic / paleolithic / high protein / weight loss. * Any known issues with blood taking. * Any known bleeding disorders. * Any known allergy to olives, inability to tolerate gluten or multiple allergies/intolerances that would significantly limit food intake. * Average alcohol use of \>21 glasses per week for men and \>14 glasses per week for women (on average for the last six months). * History of psychiatric illness including intellectual disability, schizophrenia, bipolar disorder, severe, active depression and alcoholism. * Neurologic conditions such as vascular dementia, movement disorders, history of conditions such as anaemia and cancer in the last five years, renal or liver failure, malignant tumours, or organ transplant. * Coffee consumption greater than 5 cups per day. * Body mass index \> 35 kg/ m2. * Not taking a stable dose of statins for at least 3 months before the recruitment visit. Taking antibiotics in the 1 week preceding the recruitment visit. * Pregnancy or lactation. * Participation in another clinical trial during the last 30 days prior to the recruitment visit. * Subject taking supplements that may affect lipoprotein metabolism, \>1 g of fish oil/day, antioxidant supplements, cannabidiol (CBD) oil.