Last year, scientists from The Chinese University of Hong Kong found a positive association between high consumption of tea (Camellia sinensis) and longer telomere length – a marker of younger “biological age” – and living an average of five years longer, but it was unclear just how much of an impact was made by the tea.
Now scientists from Hong Kong Polytechnic University have discovered, through a cell culture study then followed by a controlled trial of supplementation in humans, that drinking two cups of green tea daily may offer notable DNA protection from oxidation.
Writing in the September issue of British Journal of Nutrition, the study’s authors state that the “genoprotective effects of green tea lend support to its use as a functional food and provide scientific evidence for the more confident recommendation of regular intake of green tea for health promotion.”
In the in vitro trial, the scientists prepared an infusion of tea that was used to treat human immune cells. The cells were then immediately exposed to hydrogen peroxide, a highly reactive oxidant, which showed a significant decrease in DNA damage.
In the single-blinded, crossover trial, 18 healthy, nonsmoking adults (ages 35 to 50) drank two cups (150 mL) of either freshly prepared green tea (Longjing or screw-shaped) or hot water (as a control) daily. All subjects randomly received their tea or water for four weeks, then had six weeks of washout period before starting on the next four weeks of tea or water.
The researchers collected blood samples and tested cells before and after supplementation when exposed to hydrogen peroxide. Tea drinkers had a 30 to 35 percent decrease in DNA damage.
Despite antioxidant content of green tea, the authors write that this study found no evidence of whole-body oxidative stress reduction in humans as measured by a urine biomarker. However, the study helps establish that drinking green tea delivers a targeted “antioxidant” action protecting cells against oxidation.
Green tea’s protective effects are thought to be dependent on its content of antioxidant polyphenols, which include its main polyphenol, epigallocatechin gallate (EGCG). Numerous studies in animals and humans have linked EGCG to positive health outcomes including better weight management, cellular health, heart health, and even longer life. This particular study did not investigate benefits of supplementation with EGCG as a green tea extract or benefits beyond protection of cell DNA.
Chan R, Woo J, Suen E, Leung J, Tang N. Chinese tea consumption is associated with longer telomere length in elderly Chinese men. Br J Nutr. 2010 Jan;103(1):107-13. Epub 2009 Aug 12.
Han KC, Wong WC, Benzie IF. Br J Nutr. 2010 Sep 1:1-8. Genoprotective effects of green tea (Camellia sinensis) in human subjects: results of a controlled supplementation trial.