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Ask the Doc: Grape Seed Extract and Green Tea


By Stephen Z Fadem, MD, FASN, AAKP Medical Advisory Board Chair

Grape seed extracts come from grapes – as do wine and vinegar - all touted to have distinct health benefits.  A small study was done in Tunisia comparing grapeseed extract with a placebo. It was a randomized trial that lasted for six months. Although the study size was very small it did show a significant increase in plasma catalase and superoxide dismutase. It also showed a significant decrease in protein carbonylation. These large words mean that it had antioxidant properties, and antioxidants help preserve kidney function.  Although the GFR did not change in the placebo group, there was improvement in the group treated with grape seed extract. This is a very small study, and only looked at patients over a short period of time. Although safe over this time period, one cannot claim long term effectiveness until a larger study is performed. This was published in 2016 in a low impact journal and no follow up study has yet been performed. Thus, although it was demonstrated in this study to be safe, one cannot claim that grapeseed extract as an accepted therapy. It falls in the category of many other studies that are not harmful with judicious use, but without a large clinical trial to support evidence-based use.(1)

Another product with similar characteristics is green tea. Green tea is a very popular product that is used in ceremonies in Japan and China and was historically acclaimed as promoting longevity. It was popular among the ancient emperors of the Tang, Song and Ming dynasties who were aware of the Hangzhou area (West Lake) in China, known for its longjing (Dragon Well) tea with special powers. In the 16th century a special process to stop oxidation was introduced – giving us the unfermented green tea we know today. But does science support the use of green tea, or it this just an enchanted fable? Green tea is composed of polyphenol chemicals that are referred to as catechins, the most abundant of which is epigallocatechingallate (EGCG). EGCG has many properties - it blocks oxidation  and is being seriously look at for its properties against Alzheimers Disease diabetes and cardiovascular disease(2). It has also been shown to have anticarcinogenic properties (3). Phase 1 studies at MD Anderson Cancer Center showed that consuming green tea is very safe (4), and further studies have confirmed its safety. Definitive randomized controlled trials in humans are lacking to show that it is an effective therapy (5).

With respect to the kidneys, there have been specific studies that discuss its potential benefits. Most of these studies are in animals, and there are relatively few clinical studies in humans. Several questions need to be addressed, namely how to assure that the tea we swallow will make it to the target site in the kidney without being degraded (6).

For now, it remains a popular supplement that is used by millions, but largely without evidence.


1.             Turki K, Charradi K, Boukhalfa H, Belhaj M, Limam F, Aouani E. Grape seed powder improves renal failure of chronic kidney disease patients. Excli j. 2016;15:424-33.

2.             Chakrawarti L, Agrawal R, Dang S, Gupta S, Gabrani R. Therapeutic effects of EGCG: a patent review. Expert Opinion on Therapeutic Patents. 2016;26(8):907-16.

3.             Shirakami Y, Shimizu M. Possible Mechanisms of Green Tea and Its Constituents against Cancer. Molecules. 2018;23(9).

4.             Pisters KM, Newman RA, Coldman B, Shin DM, Khuri FR, Hong WK, et al. Phase I trial of oral green tea extract in adult patients with solid tumors. J Clin Oncol. 2001;19(6):1830-8.

5.             Hu J, Webster D, Cao J, Shao A. The safety of green tea and green tea extract consumption in adults - Results of a systematic review. Regul Toxicol Pharmacol. 2018;95:412-33.

6.             Kanlaya R, Thongboonkerd V. Protective Effects of Epigallocatechin-3-Gallate from Green Tea in Various Kidney Diseases. Advances in Nutrition. 2019;10(1):112-21.