BioEd Online

Exercise and caffeine combine to fight skin cancer, researchers say. Mice that mix the stimulant with daily running fight the cell damage caused by ultraviolet light better than animals that merely run or drink caffeine-laced water.

"We think the caffeine is doing considerably more than exercise alone," says Allan Conney, a biologist at Rutgers University in New Brunswick, New Jersey who led the study, published in Proceedings of the National Academy of Sciences¹.

Skin cancers triggered by sunlight, such as squamous cell carcinoma, are the most common cancers in the United States, responsible for more than 1 million cases a year, according to the American Cancer Society.

One cup or two

Previous studies in mice have shown that drinking caffeinated tea reduces the number of skin tumours, and that running after exposure to ultraviolet light boosts programmed cell death, protecting against skin cancer. In both studies, the rodents had less fat beneath their skin, suggesting a link between cancer and body fat.

To see if the trends held for caffeine and exercise together, Conney's team gave hairless mice caffeinated water and access to a running wheel. Other sets of mice got either caffeine or a running wheel, or neither.

Both mice on caffeine and unstimulated animals given exercise wheels ran about 3.5 kilometres per day. "It's more than a walk in the park," says Conney.

After two weeks, the researchers exposed the mice to ultraviolet light, causing sunburn and DNA damage that can lead to skin cancer.

The skin cells of mice that both exercised and drank caffeine showed the highest levels of programmed cell death, also called apoptosis, where damaged cells commit suicide. These mice also had more cells with two proteins key to the process, caspase-3 and phospho-p53.

But more caffeine does not necessarily mean less cancer. Sporty mice that drank the human equivalent of three to five cups of coffee a day had fewer apoptotic cells than mice that drank an equivalent of one or two cups.

Together, caffeine and exercise helped mice lose more flab than the mice in the other treatments. The animals weighed the same on average, but the caffeinated runners had less fat under their skin. Conney thinks that fatty tissue secretes molecules that encourage cancer. Surgically removing fat is known to boost apoptosis in sunburned skin cells (see 'Stay trim to cut cancer risk').

Cancer connection

It's too soon to say whether people should swig triple espressos on the treadmill, says Hasan Mukhtar, a skin-cancer expert at the University of Wisconsin in Madison. "It remains to be seen how this could be translated back to human patients, but the idea is good," he says.

Some epidemiological studies have linked caffeine or exercise to decreases in skin, liver and breast cancer.

"We need carefully controlled human studies," says Conney, a two-cups-a-day coffee drinker and an occasional athlete. "I do try to exercise. Do I enjoy it? I'm not so sure."