A large body of scientific literature illustrates the protective quality of green tea catechins and polyphenols. However, these studies often investigate the protection provided by high concentration extracts, which have a green brown colour and can stain, making them impractical as cosmetic ingredients.
Low concentrations may be effective
Recent research from scientists in Switzerland has looked at the effects of applying low concentrations of green tea extracts over a sustained period of time.
According to the study, led by Dr Christian D. Mnich from the University Hospital of Zurich, topical application of the green tea extract at 0.4 per cent over a five week period exhibited significant photochemoprotective effects.
During the study period 18 subjects applied the green tea containing extract (commercially available as OM24 from Switzerland-based company Omnimedica) and a placebo to the skin of the buttocks, chosen as it is protected from UV rays.
Subjects applied the lotions three times a day for 34 days, and participants were exposed to UVB rays between two and three hours after application.
According to the researchers there was no significant difference in erythema (skin reddening) between the skin treated with the placebo and the treatment.
However, the scientists explained that UV-induced erythema is a limited parameter to quantify damage as it does not always link to p53 expression (a tumour suppressor protein that is induced in cells by UV radiation).
In contrast, treatment with the green tea extract reduced the number of UV-induced p53 positive keratinocytes by 31.9 per cent on day six and by 36.3 per cent on day 34.
The researchers did note however, that the green tea extract did not appear to affect the formation of thymidine dimers – DNA lesions most commonly caused by UV radiation.
When lesions such as these go unrepaired they can lead to the formation of skin cancer, and it is the tumour suppressor protein p53 that is often involved in the repair process.
If the green tea extract was working as a sunscreen, one would expect the number of UV-induced lesions to decrease. As this is not the case, the researchers concluded that the protective effect (as illustrated by the smaller number of p53 positive keratinocytes) must be linked to other green tea extract mediated effects.
Such effects are likely to include the extract’s anti-inflammatory properties and its ability to reduce oxidative damage.
The scientists believe they have shown green tea extract to reduce UVB-induced damage at cosmetically usable concentrations, suggesting that the extract has potential as an everyday photochemopreventative agent.
Source: Experimental Dermatology2008 doi: 10.1111/j.1600-0625.2008.00765.xGreen tea extract reduces induction of p53 and apoptosis in UVB-irradiated human skin independent of transcriptional controlsChristian D. Mnich, Keith S. Hoek, Leila V. Virkki, Arpad Farkas, Christa Dudli, Elisabeth Laine, Mirjana Urosevic, Reinhard Dummer