Combined results from a human supplementation trial and an in vitro study indicated a 20 percent reduction in levels of DNA damage, while measures of whole-body oxidative stress were unaffected, say findings published in the British Journal of Nutrition.
“The results indicate that green tea has significant genoprotective effects and provide evidence for green tea as a ‘functional food’,” wrote researchers from The Hong Kong Polytechnic University.
The study adds to an ever-growing body of science supporting the potential benefits of green tea and the polyphenolic compounds it contains. Hundreds of studies report that the beverage may reduce the risk of certain cancers, aid weight management, and protection against Alzheimer's.
Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent.
The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.
Led by Professor Iris Benzie, the researchers recruited 18 healthy volunteers to participate in a placebo-controlled, cross-over supplementation study. Subjects were randomly assigned to receive two cups of 1 percent green tea (‘Longjing’ green tea or ‘screw-shaped’ green tea) or water every day for 4 weeks. Six week washout periods separated each four-week intervention, and blood and urine samples were collected before and after each intervention.
Analysis of these bodily fluids showed a 20 percent reduction in DNA damage, measured using the formamidopyrimidine glycosylase (Fpg) enzyme-assisted comet assay.
For the in vitro study, the researchers pre-incubated human blood cells with green tea and then exposed these cells to the oxidising agent hydrogen peroxide (H2O2). “In vitro testing results of tea-treated cells showed increased resistance of DNA to the challenge,” they stated.
On the other hand, the human study showed no changes in urine levels of 7,8-dihydro-2-deoxyguanosine (8-oxodG), reported to be “a biomarker of whole-body oxidative stress”.
At the start of this year, scientists from the Chinese University of Hong Kong reported that the cells of regular tea drinkers may have a younger biological age than cells from non-drinkers.
By looking at the length of telomeres, DNA sequences at the end of chromosomes that shorten as cells replicate and age, the Chinese researchers reported that the telomeres of people who drank an average of three cups of tea per day were about 4.6 kilobases longer than people who drank an average of a quarter of a cup a day.
This average difference in the telomere length corresponds to “approximately a difference of 5 years of life”, wrote the Hong Kong-based researchers (British Journal of Nutrition, Vol. 103, pp 107-113).
Source: British Journal of Nutrition
Published online ahead of print, doi:
“Genoprotective effects of green tea (Camellia sinensis) in human subjects: results of a controlled supplementation trial”
K. C. Hana1, W. C. Wonga1 and Iris F. F. Benzie