The effects of green rooibos tea extract on anxiety levels (REAL) study

Anxiety disorders affect ~4% of the global population, with prevalence rising 55% from 1990–2019 and a further 25.6% during COVID‑19. Only ~25% receive treatment. Interest in nutraceuticals is growing. Rooibos (Aspalathus linearis) is the only known food source of aspalathin. Preclinical studies suggest antioxidative, anti‑inflammatory, and neuroprotective effects. Aspalathin may inhibit enzymes in cortisol biosynthesis, modulating HPA‑axis activity relevant to anxiety. No human RCT has investigated green rooibos extract for anxiety. This trial aims to evaluate its effects on anxiety in adults with mild‑to‑moderate anxiety.

Materials and Methods

Design: Single‑centre, pilot, double‑blind, RCT. 8‑week intervention: active (green rooibos extract; 19.25 mg aspalathin/capsule) or placebo (maltodextrin). Dose: one capsule daily (week 1), two capsules daily (weeks 2–8) (~40 mg aspalathin/day, ~6 cups of tea).

Participants: 60 adults, 18–65, mild‑to‑moderate anxiety (BAI 11–25). Exclusions: BMI ≥35, BP ≥160/95, anxiolytics/antidepressants/sleep/CV/GI medications, chronic disease, pregnancy/lactation, recent antibiotics/probiotics.

Randomisation: Stratified by age/gender, 1:1 ratio, blinded.

Procedures: Four clinic visits. Questionnaires, actigraphy (MotionWatch 8), saliva collection, anthropometrics, VO2max, and physiological measurements.

Primary Outcome: DASS‑21 anxiety subscale change from baseline.

Secondary Outcomes: HRV (Polar H10), salivary cortisol and alpha‑amylase, actigraphy sleep variables, 3‑day food records, DASS‑21 depression/stress subscales, anthropometry, VO2max, AUDIT‑C, PROMIS sleep quality.

Analysis: Intention‑to‑treat; linear mixed‑effects models. Significance P<0.05; false discovery rate control; responders defined as ≥15% reduction.

Discussion

Clinical Utility: Persistent anxiety is linked to neuroendocrine, autonomic, and immune dysregulation, increasing CVD and diabetes risk. Green rooibos extract could offer an accessible adjunct.

Mechanisms: Aspalathin may influence HPA‑axis and cortisol. Salivary cortisol/alpha‑amylase and HRV provide stress biomarkers. Cardiorespiratory fitness, sleep, and diet are contextual factors. Rooibos may have prebiotic activity.

Nutraceutical Development: Encapsulated extract is cost‑effective and scalable. If effective, it could support functional food development.

Limitations: Focus on subclinical‑to‑moderate anxiety, not diagnosed disorders. Larger trials needed for clinical populations and long‑term safety.

Conclusions

This trial will provide preliminary evidence on green rooibos extract for mild‑to‑moderate anxiety. If effective, it could offer an accessible, well‑tolerated adjunct to current management. Further research is needed for clinical validation and long‑term outcomes.

Full text:

https://www.xiahepublishing.com/2472-0712/ERHM-2025-00088

The study was recently published in the Exploratory Research and Hypothesis in Medicine.

Exploratory Research and Hypothesis in Medicine (ERHM) publishes original exploratory research articles and state-of-the-art reviews that focus on novel findings and the most recent scientific advances that support new hypotheses in medicine. The journal accepts a wide range of topics, including innovative diagnostic and therapeutic modalities as well as insightful theories related to the practice of medicine. The exploratory research published in ERHM does not necessarily need to be comprehensive and conclusive, but the study design must be solid, the methodologies must be reliable, the results must be true, and the hypothesis must be rational and justifiable with evidence.

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