This randomized, double-blind, placebo-controlled study evaluates the efficacy and safety of an 8-week probiotic supplementation (Lactobacillus plantarum LP140 and Bifidobacterium breve BB010 in total daily dose 1 × 10¹⁰ CFU or matching placebo) in reducing perceived stress and anxiety, and improvement related psychological parameters in healthy university students during the examination period. The primary outcome is the change in Perceived Stress Scale (PSS-10) score at week 5 and week 8 of interevention compared to placebo. The secondary outcomes are the changes in DASS-21 subscales (Stress, Anxiety, Depression), State-Trait Anxiety Inventory - State version scale (STAI-S), Sense of Coherence Scale (SOC-29), Pittsburgh Sleep Quality Index (PSQI), self-reported gastrointestinal symptoms (Likert scale) and incidence of adverse events during the 8-week lasting interventional study.
Inclusion Criteria
- Male or female students aged 18-40 years
- At least moderate stress (DASS-21 Stress score ≥10)
- Mild anxiety (DASS-21 Anxiety score 6-13)
- No clinical depression (DASS-21 Depression score ≤9)
- Willingness to maintain usual diet, physical activity, and intake of caffeinated beverages during the study
- Written informed consent
Exclusion Criteria
- Irritable bowel syndrome (Rome IV criteria) or any chronic intestinal disease (including celiac disease)
- Known food allergies, immunodeficiency disorders, or immunosuppressive treatment
- Antibiotic use within 4 weeks prior to screening
- Any psychiatric illness within the past 5 years
- Any malignant disease or autoimmune or allergic diseases (e.g., atopic dermatitis, asthma)
- Use of systemic psychotropic medications or steroids; use of topical corticosteroid creams within 4 weeks prior to screening
- Pregnancy, breastfeeding, or plans to become pregnant during the study
- Probiotic or prebiotic consumption or planned dietary changes within 4 weeks prior to screening
- Heavy caffeine consumption (\>4 cups of 300 mL coffee per day)
- Drug or alcohol addiction or regular use of recreational drugs
- Smoking more than 10 cigarettes per day