Tea contains chemicals called polyphenols that appear to block the formation of nonmelanoma skin tumors, the researchers say. Unlike sunblock, which prevents the skin from absorbing harmful ultraviolet (UV) light, tea polyphenols work after the skin is exposed to excessive sunlight. The compounds, which are found in both black and green teas, inhibit a newly discovered chemical pathway -- involving an enzyme called JNK-2 -- that appears to play a key role in the development of tumors, they say.
The scientists found that the JNK-2 (or "junk-2") enzyme increases after the skin is exposed to sunlight and stays elevated in the skin of those exposed to excess amounts of sunlight. When JNK-2 stays elevated, skin cancers are more likely to develop, they say.
In laboratory studies using mouse models of skin cancer in which the mice were exposed to ultraviolet light, the researchers demonstrated that topical exposure to green tea polyphenols decreased levels of the enzyme, which in turn delays or blocks the skin's response to UV light. Similar polyphenols are also found in black tea.
"We feel this is an important step in improving the prevention of skin cancer," says study leader Dr. Zigang Dong, M.D., a professor at the university and executive director of the school's Hormel Institute. "Topical application of certain tea polyphenols appears to block a key process that leads to skin cancer."
Dong and his research team are currently working to optimize the effectiveness of tea components against cancer. Designed to be applied after exposure to excessive sun, the skin cream could be used alone or combined with sunscreen to help maximize cancer protection. Human testing of the proposed skin cream could begin in a few years, he says.
Dong does not know yet if the tea chemicals will inhibit melanoma, the least common but most deadly type of skin cancer. More studies are needed, he adds. Dong also acknowledges that there may be other cancer-promoting pathways in the skin that are inhibited by tea but says further investigation is needed to determine that.
Other researchers have previously demonstrated that drinking tea, particularly green tea, may be effective against skin cancer. They believe that this is mainly due to tea's high level of antioxidants, which destroy free radicals that are thought to damage a cell's DNA and trigger the cancer process. But Dong feels a topical application is likely to be a better approach than drinking tea.
"Drinking tea may help, but you'd have to drink a large amount to accumulate in the skin, perhaps as many as 10 cups a day. It's easier to concentrate it in a cream form, and it's probably more effective," says Dong.
There are some skin creams already on the market that contain tea compounds, Dong says. However, these products are unlikely to have undergone testing and are likely to contain non-uniform amounts of tea antioxidants, he adds.
Skin cancer is the most common type of cancer in the United States, with about a million new cases reported each year. People can reduce their risk by avoiding excessive sun exposure, avoiding sunlamps and tanning booths, and using a strong sunscreen.
Funding for this study was provided by the National Cancer Institute and the Hormel Foundation.
The paper on this research, AGFD 59, will be presented at 1:30 p.m. on Monday, Sept. 8, at the Javits Convention Center, Room 1AO6, during the "Tea and Health" symposium.
Zigang Dong, M.D., Dr.P.H., is a professor at the University of Minnesota in Austin and executive director of its Hormel Institute.
-- Mark T. Sampson