- Indications with possible efficacy:
Improve cognitive performance
- Indications with possible, but poorly documented efficacy:
- Other indications with no proof of efficacy:
Cancer prevention (common use)
Cardiovascular protection (common use)
Improve cognitive performance
Parkinson's disease (prevention)
- Risk of Drug Interactions:
- Adverse Effects:
Part of the plant used: leaves
Tea is made from the leaves of the Camellia sinensis, a plant that is native to Eastern Asia. Tea leaves contain many compounds which determine efficacy. Compounds include caffeine (10 to 80 mg of caffeine per cup) and polyphenols (50 to 150 mg of catechins per cup). Catechins are substances that have antioxidant and anti-inflammatory properties. Epigallocatechin-gallate (EGCG) is a main constituent of tea catechins.
Green tea is traditionally ingested as a warm beverage.
Directions for use
Green tea extracts should be taken with food.
- Improving cognitive functions
The effectiveness of green tea is connected to its caffeine content.
Infusion - on average, 1 cup contains 60 mg of caffeine.
Green tea helps lower triglyceride and cholesterol levels.
Extract - 1200 to 2300 mg per day
Catechins - 491 to 714 mg per day
- Cancer prevention
The effect is proportional to the amount of tea ingested and is the result of its catechin content.
Infusion - 3 to 10 cups per day
- Cardiovascular protection
Catechins - 400 to 716 mg per day
- Adverse effects
There are few adverse effects associated with usual doses of green tea. Most side effects are due to its caffeine content. High doses of caffeine may cause headache, dizziness, stomach upset, nausea, vomiting, agitation, insomnia and shaking. Liver problems have also been reported in a small number of people who took concentrated green tea extracts. It is thus recommended to consult a health care practitioner if symptoms of liver trouble such as abdominal pain, dark urine, or jaundice occur.
Patients with liver problems should avoid green tea. Use with caution in patients with anemia, anxiety and hypertension.
Green tea is not recommended for those taking oral anticoagulants, antiplatelets or anti-inflammatories. Green tea interacts with several drugs. It is therefore recommended that you speak to your pharmacist to see whether it is compatible with the drugs you are presently taking. It may also prevent the absorption of non-animal sources of iron.
- Pregnancy and breastfeeding
Since green tea contains caffeine, women who are pregnant or breastfeeding should use with moderation.
In 2004, Canada adopted new regulations that control the manufacturing, packaging, labeling and importing of natural health products. The new regulations also include an adverse reaction reporting system. Products that conform to the regulation's criteria are identified with a natural product number (NPN) and can be legally sold in Canada. This number indicates that the product meets specific criteria for safety and purity, not that it is effective for any indication.
Medicinal plant contents vary naturally from plant to plant - just as fruits from the same package may vary in taste and texture. There is no standard to measure the active content of each plant. Thus, efficacy of natural products should be expected to vary from brand to brand as well as from bottle to bottle of the same brand.
For more information about the Natural Health Products Regulations, or to check if a product has been assessed, visit the Health Canada website at http://www.hc-sc.gc.ca/dhp-mps/prodnatur/index-eng.php.
- Natural Medicines Comprehensive Database, Therapeutic Research Faculty, 2010
- Passeportsanté.net. Thé vert. www.passeportsante.net
- Natural Therapeutics Pocket Guide, 2000-2001
- Rotblatt M. and Ziment I. Evidence-Based Herbal Medicine, Hanley & Belfus, 2002
- The Review of Natural Products, 6th Edition, 2010
- Health Canada, Natural Products Database