Green tea extract is well known for its antioxidant qualities and has long been regarded as an ingredient that might help protect the skin against UV damage. However, topical application of high concentration green tea extracts can stain the skin, making it impractical for skin care formulations.
The ability to stain, combined with the increasing interest in ‘beauty from within’, has led to the release of a number of green tea extracts aimed at both the nutritional supplement and the nutricosmetic markets.
No significant difference between placebo and green tea
This latest study, which the researchers claim is the largest double-blind, randomized, placebo-controlled clinical trial on the subject, could be bad news for those wishing to enter into the cosmetics market with the extract.
The research, conducted by scientists at Stanford University, California, in collaboration with cosmetics company Nu Skin which funded the study, looked at the effects of oral green tea supplements on a number of characteristics associated with UV aging. These included fine and coarse wrinkles, pore size, erythema (skin redness) and collagen levels.
According to the study authors, a number of in vitro and animal studies have suggested green tea polyphenols stimulate epidermal regeneration in aged keratinocytes and the aim of this study was to investigate the long term effects of supplementation.
The study included 56 women between the ages of 25 and 75, half of which were randomly assigned the placebo and half the green tea capsules containing 250mg of polyphenols (70 per cent of which were catechins).
Participants were asked to take one capsule twice daily for 24 months, and assessments on the state of the skin were performed at six monthly intervals by a dermatologist and the subjects themselves. In addition, at the beginning and end of the study period samples were taken of sun exposed skin on the upper arm.
According to results from the dermatologist, who like the study participants was unaware who was receiving the treatment, overall solar damage decreased in the green tea group but not in the placebo group at six months; however, these benefits did not seem to stand the test of time as at 24 months they were not present.
In addition, the dermatologists examinations did not bring up any significant differences at any time point between the green tea and the placebo group in a number of parameters including fine and coarse wrinkling, irregular pigmentation and pore size.
Both placebo and green were associated with imrpovements
Similarly, histological analysis did not show any significant differences between the green tea and the placebo groups. But, interestingly, both groups showed significant improvement at 24 months in overall solar damage. This, the team suggested, could be down to the effect that participating in the study had on subjects’ behaviour in the sun.
However, green tea supplementation seemed to bring about improvements earlier than the placebo, but no satisfactory reason could be found by the team.
“Unfortunately, we did not have the subjects keep a detailed diary of their sun exposures or other activities, which may have enabled us to determine whether these external factor could explain the improvement in overall solar damage and erythema and telangiectasis in both groups,” wrote the authors.
They conclude that after two years of supplementation with oral green tea pholyphenols “there were no statistically significant differences in the clinical or histological parameters of phtoaging”.
Source: Journal of Dermatologic Surgery
July 2009, Volume 35, Issue 7, pages 1057- 1064
A two-year, double-blind, randomized placebo-controlled trial of oral green tea polyphenols on the long-term clinical and histological appearance of photoaging skin
Roohina Junjua, Claudia Munoz, Emily Gorell, Wingfield Rehmus, Barbara Egbert, Dale Kern and Anne Lynn S. Chang