Effective aftersun: Mice given similar levels of caffeine to daily coffee drinkers – and the opportunity to excercise – were much more effective at striking out sunburn-damaged cells.

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SYDNEY: The fight against skin cancer may have found two unlikely allies, with scientists finding that caffeine and exercise work together to decrease the damage caused by the Sun's rays.

Experts from Rutgers, the State University of New Jersey, in the U.S., made the finding after previously revealing that caffeine or exercise alone act to protect mice against cancer caused by the UVB component of the sun's ultraviolet radiation.

"Our studies in mice suggest that ingestion of moderate amounts of caffeine and voluntary exercise will strongly enhance the killing of UVB damaged cells and inhibit UVB-induced skin cancer," said oncologist Allan Conney.

Cancer stopper

Conney led the team that report the discovery today in the U.S. journal Proceedings of the National Academy of Sciences.

UVB light damages our DNA, increasing the risk of affected cells becoming cancerous. Anything that kills off these 'UVB-induced sunburn cells' is actually good news, as it stops pre-cancerous cells from turning nasty.

After initially exposing a special breed of hairless laboratory mice to UVB radiation, Lu and colleagues tested three treatments for their ability to kill off the sunburnt cells. Over a two-week period the mice were given caffeine mixed with drinking water, voluntary exercise on a running wheel, or a combination of both.

On their own, caffeine or exercise killed about twice as many sunburnt cells as mice given neither treatment. But five times as many sunburnt cells died on the mice treated with both caffeine and exercise in combination, as on the mice treated with neither.

Significantly, the increase in cell death was limited to the pre-cancerous sunburnt cells, with skin cells that were not damaged by UVB radiation unaffected by the treatments.

The mice were given between 0.1 and 0.4 mg per ml of caffeine in drinking water - similar to that in the blood plasma of most coffee drinkers (one to four cups per day). But, intriguingly, the experts found that a combination of caffeine and exercise was more effective at the lower caffeine dose of 0.1 mg/ml.

From mice to man

Previous epidemiological studies have shown that increased exercise is associated with a lower risk of melanoma, colon cancer, breast cancer, and advanced prostate cancer. In other studies researchers have found that caffeine, via coffee consumption, was associated with a lower risk of non-melanoma skin cancer, liver cancer, and breast cancer.

It remains to be seen just how caffeine and exercise interact at the molecular level to kill of pre-cancerous cells. Lu's team now plan on examining the effect of different types of exercise.

The question that needs to be resolved before we can all add a cappuccino to our pre-exercise stretch routine is whether the results will translate from mice to humans.

"We believe that these treatments may also inhibit sunlight-induced skin cancer in humans, but clinical studies are needed to see if we can extrapolate our mouse studies to people," Conney said.