Is green tea safe?
""No severe adverse effects have been reported in association with medicinal use of green tea"
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Green tea, as a popularly consumed beverage, is relatively non-toxic (ref 37). No severe adverse effects have been reported in association with medicinal use of green tea (ref 39). People with known allergy or hypersensitivity to caffeine or tannin should avoid green tea. Consumption of high doses of green tea or green tea extract (equivalent to five litres per day) may cause nausea, vomiting, abdominal bloating and pain, dyspepsia, flatulence, and diarrhoea (ref 38). Excess consumption of caffeine from green tea may also cause central nervous system stimulation such as dizziness, insomnia, tremors, restlessness and confusion, and diuresis (increasing urine output), irregularities in heart rate, and psychomotor agitation (ref 38). Therefore, pregnant women, nursing mothers and patients with cardiac problems are usually advised to avoid or limit their intake to two cups daily (ref 39). In general, the stimulatory effect from green tea is considerably less than that of coffee (ref 37).
Human studies did not find severe adverse effects among volunteers who took 15 green tea tablets per day (2.25g green tea extracts, 337.5mg EGCG, and 135mg caffeine) for six months (ref 39,40). A randomized, placebo-controlled trial concluded that it is safe for healthy individuals to take green tea polyphenols in amount equivalent to the EGCG content in 8 to 16 cups of green tea once a day or in divided doses twice a day for four weeks (ref 40).
References
37. Brown MD. Green tea (Camellia sinensis) extract and its possible role in the prevention of cancer. Altern Med Rev 1999;4(5):360-70.
38. The Natural Medicines Comprehensive Database. http://www.naturaldatabase.com/ accessed by 8 August 2005.
39. Fujiki H, Suganuma M, Okabe S, Sueoka E, Suga K, Imai K, Nakachi K, Kimura S. Mechanistic findings of green tea as cancer preventive for humans. Proc Soc Exp Biol Med 1999;220(4):225-8.
40. Chow HH, Cai Y, Hakim IA, Crowell JA, Shahi F, Brooks CA, et al. Pharmacokinetics and safety of green tea polyphenols after multiple-dose administration of epigallocatechin gallate and polyphenon E in healthy individuals. Clin Cancer Res 2003;9(9):3312-9.
