L-THEANINE AND MEDITERRANEAN DIET ON RBD, GI FUNCTION, AND INFLAMMATION IN PARKINSON'S DISEASE

THE EFFECT OF L-THEANINE SUPPLEMENTATION ON REM SLEEP BEHAVIOR DISORDER, GASTROINTESTINAL FUNCTION, AND INFLAMMATORY MARKERS IN PARKINSON'S DISEASE

Parkinson's disease is a progressive neurological disorder associated with severe dopaminergic neuron loss in the substantia nigra pars compacta. The decrease in dopamine cells in the gut in Parkinson's disease negatively affects bowel movements, and constipation is a common condition. Impairment of the intestinal barrier increases inflammation. Reactive oxygen species increase, and intestinal homeostasis changes. Alpha-synuclein levels increase in the gut. L-theanine is the most abundant amino acid in green tea leaves. Parkinson's patients exhibit increased oxidative stress along with decreased activity of glutathione peroxidase, superoxide dismutase, and catalase. L-theanine is believed to increase the activity of these enzymes and reduce oxidative stress. L-theanine administration has been found to increase total short-chain fatty acids in stool. Furthermore, it is suggested that L-theanine inhibits imbalances in oxidative stress and inflammatory responses by reducing inflammatory factors such as TNF-α, IL-6, and IL-1β. REM sleep disturbance is also a common problem in Parkinson's disease. Studies have shown that following L-theanine treatment, participants' Pittsburgh Sleep Quality Index (PSQI) scale scores improved. The gut microbiota regulates sleep and neurological states via the microbiota-gut-brain axis. L-theanine supplementation appears to be able to regulate gut bacterial composition to suppress neurotransmitters, cytokines, and other metabolites to regulate sleep. The protective effects of L-theanine administration on increased dopamine and other neurotransmitters, microbiota, sleep, and antioxidant enzymes may offer a glimmer of hope regarding its beneficial role in Parkinson's disease.

Study Overview

• Status: Recruiting
• Conditions: Parkinson Disease (PD)
• Intervention / Treatment: Dietary supplement: Dietary Supplement; Other: Control group (placebo)

• Study Type: Interventional
• Enrollment (Estimated): 52
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Rüken A Samancı; Phone Number: +90 543 939 15 94; Email: rasamanci@medipol.edu.tr

Study Locations

• Turkey (Türkiye)
  • Istanbul, Turkey (Türkiye)
    • Recruiting
    • Medipol Mega Hospital
    • Contact: Rüken A Samancı; Phone Number: +90 543 939 15 94; Email: rasamanci@medipol.edu.tr
    • Principal Investigator: Gözde Ülfer
    • Principal Investigator: Eren Toplutaş

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

Patients diagnosed with Parkinson's Disease and classified as stage 1 according to the Hoehn-Yahr Staging (HYA), Patients without communication impairment (aphasia) Participants who sign the Informed Consent Form and volunteer to participate in the study Absence of dementia and Mini Mental State Examination (MMSE) score > 24 Living in the same household with a healthy spouse/partner Not taking prebiotic, fiber, probiotic, herbal, or high-dose vitamin or mineral supplements that may affect inflammation during the pre-onset period and throughout the study protocol

Exclusion Criteria:

Patients with a history of severe heart, lung, liver, or kidney failure, primary psychiatric, developmental, or other neurological disease Patients using sedative/hypnotic medications Individuals consuming more than 200 mg of caffeine per day (approximately 2-3 cups of tea or 1 cup of coffee) Patients who smoke and consume alcohol Having undergone surgery related to bowel health Having a chronic infectious bowel disease Having a congenital bowel anomaly Using probiotics, antifungals, and/or antibiotics within the last three months Individuals with an autoimmune disease or weakened immune system Self-reported alcohol or drug use within the last 3 months Current use of over-the-counter medications, supplements, foods, and/or beverages that may affect stress, sleep, cognition, and/or mood Inability to swallow the study supplement due to swallowing anxiety Receiving treatment for a GI disease or condition diagnosed by a doctor other than constipation, gastroparesis, gastroesophageal reflux disease, or diverticular disease Positive results for human immunodeficiency virus (HIV) or Hepatitis B/C. Current history of active conditions of inflammatory bowel disease, irritable bowel syndrome, colitis, celiac disease, short bowel syndrome, colostomy, colectomy, gastrointestinal fistula, or strictures.

Recent or current use of any antibiotic (within 4 weeks prior to the start of the study) Use of enemas or suppositories to relieve constipation Good adherence to the Mediterranean diet in the pre-start period according to the 14-item Mediterranean Diet Assessment Tool (score >6)

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Supportive Care
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: L-Theanine + Mediterranean Diet; 200 mg of L-theanine supplement will be given daily. A Mediterranean diet will be followed.	Dietary supplement: Dietary Supplement; L-theanine supplementation combined with Mediterranean diet for 4 weeks.
Placebo Comparator: Placebo + Mediterranean Diet; 200 mg of placebo corn starch will be given daily. A Mediterranean diet will be followed.	Other: Control group (placebo); Placebo combined with Mediterranean diet for 4 weeks.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
RBD Screening Questionnaire (RBDSQ) score	Change in RBD Screening Questionnaire (RBDSQ) score from baseline to week 4. RBDSQ is a 13-item self-reported questionnaire assessing REM sleep behavior disorder symptoms. Scores range from 0 to 13; higher scores indicate greater RBD severity.	from baseline to week 4

Collaborators and Investigators

• Sponsor: Medipol University

Study record dates

Study Major Dates

• Study Start (Actual): May 2, 2026
• Primary Completion (Estimated): September 25, 2026
• Study Completion (Estimated): October 20, 2026

Study Registration Dates

• First Submitted: June 28, 2026
• First Submitted That Met QC Criteria: June 28, 2026
• First Posted (Actual): July 6, 2026

Study Record Updates

• Last Update Posted (Actual): July 6, 2026
• Last Update Submitted That Met QC Criteria: June 28, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: nutrition; inflammation; Parkinson's disease; REM sleep behavior disorder
• Additional Relevant MeSH Terms: Synucleinopathies; Brain Diseases; Central Nervous System Diseases; Nervous System Diseases; Mental Disorders; Pathologic Processes; Neurodegenerative Diseases; Sleep Wake Disorders; Movement Disorders; Parkinsonian Disorders; Basal Ganglia Diseases; Parasomnias; REM Sleep Parasomnias; Pathological Conditions, Signs and Symptoms; Inflammation; Parkinson Disease; REM Sleep Behavior Disorder; Investigative Techniques; Epidemiologic Research Design; Epidemiologic Methods; Research Design; Methods; Food; Diet, Food, and Nutrition; Physiological Phenomena; Food and Beverages; Control Groups; Dietary Supplements
• Other Study ID Numbers: 125S555

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No