Green Tea

Consumed for >2,000 years in China and Japan for alertness, digestive comfort, and general vitality. In Traditional Chinese Medicine, green tea is “cooling,” used to “clear heat” and support mental clarity; in Japan, daily use is part of cultural tea ceremony practices.

• Polyphenols (catechins): (typically 15–30% of dry leaf) epigallocatechin gallate (EGCG; major), epigallocatechin (EGC), epicatechin gallate (ECG), epicatechin (EC).
• Methylxanthines: caffeine (≈20–45 mg per 240 mL brewed cup; matcha higher), theobromine, theophylline.
• Amino acids: L-theanine (relaxing, attention-modulating).
• Minor constituents: flavonols (quercetin, kaempferol), minerals (K, Mn, F), volatile aromatics.

• Antioxidant/Redox-active: Catechins scavenge radicals and up-regulate endogenous antioxidant enzymes (e.g., Nrf2-linked pathways).
• Metabolic & cardiometabolic: Mild inhibition of lipid absorption; effects on LDL oxidation; small thermogenic effect (caffeine + catechins).
• Neurocognitive: Caffeine improves vigilance; L-theanine may smooth stimulant effects (attenuates jitter, promotes relaxed attention).
• Vasoactive: Modest improvements in endothelial function and blood pressure in some trials.
• Antimicrobial/anti-adhesive: In vitro activity against oral pathogens; supports oral health.

• Cardiometabolic risk markers (LDL-C, BP): Small but statistically significant improvements in LDL-cholesterol and systolic BP have been reported across RCTs of green-tea catechins/EGCG; effects are modest and hinge on dose, caffeine co-ingestion, and baseline status.
• Weight management: Cochrane review of RCTs found minimal to no clinically meaningful effect of green-tea preparations on weight loss/maintenance in overweight/obese adults. Use primarily for general wellness, not as a stand-alone slimming aid.
• Liver safety signal at high EGCG doses: Benefit–risk is favorable for brewed tea; concentrated extracts at high daily EGCG (≥800 mg/day, especially fasting) raise the risk of liver enzyme elevations/rare hepatotoxicity.
• Drug interaction potential: Green tea polyphenols can reduce the oral bioavailability of some drugs via transporter inhibition (notably OATP2B1) e.g., decreased exposure to the beta-blocker nadolol shown in clinical research and may antagonize non-heme iron absorption with meals.
• Bottom line: Best-supported outcomes are small improvements in cardiometabolic markers and general alertness/attention (caffeine ± theanine). Weight-loss effects are minor.

• Brewed green tea: 2–4 cups/day (≈400–800 mL) is a common evidence-based intake for general wellness (provides roughly 100–300 mg EGCG/day depending on leaf, brew time, and variety).
• Standardized extracts: Common label doses deliver 150–300 mg EGCG once or twice daily, with food. Avoid fasting use and avoid ≥800 mg/day EGCG, aligning with EFSA safety advice. Stop if you develop signs of liver distress (fatigue, dark urine, jaundice).

• Pre-existing liver disease or previous green-tea-extract–related liver enzyme elevations. Iron-deficiency anemia (tea with iron-rich meals can reduce non-heme iron absorption; separate by 1–2 hours).
• Pregnancy & lactation: Moderate brewed tea is generally considered compatible; avoid high-dose extracts given limited safety data and hepatotoxicity signal at high EGCG doses. Caffeine sensitivity, arrhythmias, uncontrolled hypertension, or anxiety disorders (prefer decaffeinated green tea or lower-caffeine varieties)

• Common (dose-related, usually mild): GI upset, nausea (more likely with extracts/empty stomach), nervousness/insomnia/palpitations (caffeine).
• Less common/serious: Liver enzyme elevations and rare clinically apparent hepatotoxicity linked to high-dose extracts; typically reversible after discontinuation. Dental: Enamel staining possible with heavy intake (cosmetic)

1. Green-tea catechins: safety and liver considerations; advises avoiding ≥800 mg/day EGCG, especially fasting. (EFSA summary). https://pmc.ncbi.nlm.nih.gov/articles/PMC7009618/

2. Evaluation of liver-related safety of green tea extracts used in dietary supplements. https://pmc.ncbi.nlm.nih.gov/articles/PMC5193539/

3. RCT synthesis shows little to no clinically meaningful effect on weight. https://pmc.ncbi.nlm.nih.gov/articles/PMC7116866/

4. Polyphenol-rich teas inhibit non-heme iron absorption in humans. https://pmc.ncbi.nlm.nih.gov/articles/PMC6804354/

5. Tea Overview of efficacy, safety, and interaction considerations for tea, including green tea. https://pmc.ncbi.nlm.nih.gov/articles/PMC9370301/

Green tea (Camellia sinensis) is a polyphenol-rich beverage with modest, supportive effects on cardiometabolic markers and attention, best used as part of a healthy lifestyle. Brewed tea is generally safe; however, concentrated extracts require care — take with food, avoid high daily EGCG doses (≥800 mg), and stop if liver-related symptoms occur. Be mindful of potential drug interactions (notably with nadolol and iron supplements) and caffeine sensitivity.