Can Drinking Green Tea be Good for Glaucoma?
White, Green, Oolong, and Black teas made from the leaves of Camellia Sinensis contain water-soluble polyphenols called catechins. There are four main catechins found in the leaves of Camellia Sinensis of which epigallocatechin-3-gallate (EGCG) is the most potent. One cup of green tea contains approximately 50mg of EGCG.
Less than 2% of the catechins ingested are absorbed into the bloodstream.[1] Bioavailability is increased when green tea catechins are ingested along with Quercetin[2] or fish oil.[3] Once absorbed into the bloodstream EGCG is able to pass through the blood-brain barrier.[4] There is also laboratory evidence that it penetrates the tissues of the eye.[5]
Evidence that Green Tea Catechins can be effective in the treatment of Glaucoma
No studies have been published documenting a direct IOP lowering or vision stabilizing benefit from ingestion of green tea or its extract. However, at least in laboratory rats, oral EGCG has been shown to protect the retina from damage.[6] Additionally, green tea catechins have anti-oxidant properties. This effect appears to be enhanced when green tea catechins are ingested along with Quercetin or Ginkgo biloba (which contains Quercetin).[7]
Potential Side Effects and Risks of Green Tea Catechins
When consumed as a beverage, green tea does not appear to be associated with any toxicity[8] unless upwards of five liters is consumed in a day.[9] It’s worth noting that caffeine is also present in green tea and can be associated with rapid heart rate and insomnia.[10] Green tea catechins (specifically EGCG) are generally safe and well-tolerated in doses up to 800mg.[11] Larger doses of EGCG, however, are associated with nausea. Additionally, liver toxicity has been associated with large doses of green tea extract.[12] In extremely large doses (>500mg/kg) green tea catechins have been shown to be lethal in laboratory animals.
Potential Drug Interactions with Green Tea Catechins
Most of the potential drug interactions associated with green tea are actually due to the caffeine content. When consumed in moderation or in a decaffeinated form there are very few serious reported drug interactions with green tea.
Dosage
As no human glaucoma studies have been done looking at the role of green tea catechins, it is not possible to recommend a proper dosage. I do not currently recommend taking an oral extract. However, because of its potential health benefits and lower caffeine concentration, I do recommend that my patients with glaucoma drink green tea in moderation instead of coffee.
References
[1] Warden BA, et al. Catechins are bioavailable in men and women drinking black tea throughout the day. J Nutr. (2001)
[2] Wang P, Heber D, Henning SM. Quercetin increased bioavailability and decreased methylation of green tea polyphenols in vitro and in vivo. Food Funct. (2012)
[3] Giunta B, et al. Fish oil enhances anti-amyloidogenic properties of green tea EGCG in Tg2576 mice. Neurosci Lett. (2010)
[4] Suganuma M, et al. Wide distribution of {3H}(-)-epigallocatechin gallate, a cancer preventive tea polyphenol, in mouse tissue. Carcinogenesis. (1998)
[5] Chu et al. Green Tea Catechins and Their Oxidative Protection in the Rat Eye. Journal of Agricultural and Food Chemistry, 2010; 58 (3): 1523 DOI: 10.1021/jf9032602
[6] Zhang B, Rusciano D, Osborne NN. Orally administered epigallocatechin gallate attenuates retinal neuronal death in vivo and light-induced apoptosis in vitro. Brain Res. 2008 Mar 10;1198:141-52.
[7] Jain DP, Pancholi SS, Patel R. Synergistic antioxidant activity of green tea with some herbs. J Adv Pharm Technol Res. (2011)
[8] Chow HH, 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] Pisters KM, Newman RA, Coldman B, et al. Phase I trial of oral green tea extract in adult patients with solid tumors. J Clin Oncol 2001;19:1830-8.
Jatoi A, Ellison N, Burch PA, et al. A phase II trial of green tea in the treatment of patients with androgen independent metastatic prostate carcinoma. Cancer 2003;97:1442-6.
[10] Institute of Medicine. Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations. Washington, DC: National Academy Press, 2001.
[11] Ullmann U, et al. Plasma-kinetic characteristics of purified and isolated green tea catechin epigallocatechin gallate (EGCG) after 10 days repeated dosing in healthy volunteers. Int J Vitam Nutr Res. (2004)
Chow HH, et al. Effects of repeated green tea catechin administration on human cytochrome P450 activity. Cancer Epidemiol Biomarkers Prev. (2006)
[12] Bonkovsky HL. Hepatotoxicity associated with supplements containing Chinese green tea (Camellia sinensis). Ann Intern Med 2006;144:68-71.
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