NEW YORK (Reuters Health) - Caffeine in the form of a lotion may help to prevent skin cancer, according to the results of a new study. But a separate study found that caffeine may actually promote cancer.

In the "good news" study, skin cancer was prevented in mice at risk of developing the disease if a lotion containing caffeine was applied to their skin. In the "bad news" study, when a dish of hamster cells was exposed to tumor-inducing radiation, adding caffeine appeared to inhibit the cells' ability to repair themselves, increasing their likelihood of becoming cancerous.

Both studies appear in the online Early Edition of the Proceedings of the National Academy of Sciences.

These studies add to a growing body of contradictory results about the links between caffeine and cancer. For example, one study showed that caffeine may help fight off cancer by blocking an enzyme that is crucial for cell growth, thereby potentially inhibiting the uncontrolled growth that characterizes cancer. In contrast, another report showed that drinking coffee did not reduce women's risk of developing colorectal cancer.

In the first of the two recent studies, Dr. Allan H. Conney of Rutgers, The State University of New Jersey, and his colleagues exposed mice to ultraviolet light twice a week for 20 weeks. As a result of this exposure, the mice--initially tumor-free--had an increased risk of developing skin cancers over the next several months.

Five days a week for the next 18 weeks, the researchers rubbed an inactive lotion onto the backs of some of the mice, one that contained caffeine onto the backs of others, and a lotion with the compound epigallocatechin gallate (EGCG), an ingredient of green tea, onto the rest. The investigators then measured how many tumors the mice developed.

Conney's team found that mice treated with a caffeinated lotion developed 44% fewer non-cancerous tumors and 72% fewer cancerous tumors than those given the inactive treatment. Mice that received the EGCG-filled substance had a reduction in their non-cancerous and cancerous tumors of 55% and 65%, respectively.

In the second study, Dr. Theodore Puck and his colleagues exposed hamster cells to low doses of radiation--levels similar to those found in the basements of some buildings and in mines. This type of radiation, known as alpha radiation, has been linked to the development of lung cancer.

Exposure to radiation caused a certain number of mutations--alterations to the cells' genetic material that can increase the risk of developing cancer--the authors note. Cells contain natural mechanisms to repair many of these mutations; however, when Puck and his team added caffeine to the samples, the cells were much less able to repair these mutations than when they were caffeine-free.

Speaking with Reuters Health, Puck said that researchers still do not know why caffeine might inhibit cellular repair. He added that his experiment also shows how radiation exposure can induce mutations, and recommended that investigators continue working to pinpoint the sources of this radiation, and try to eliminate them.

"We can detect sources of mutations in the environment with extremely good sensitivity," he said. "And that makes it possible to remove them from the environment."

SOURCE: Proceedings of the National Academy of Sciences 2002;10.1073/pnas.152433699, 182429899.

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