Washington ? Can adding a cup or two of coffee to the exercise routine increase protection from skin cancer? New research indicates that just might be the case.

The combination of exercise and caffeine increased destruction of precancerous cells that had been damaged by the sun’s ultraviolet-B radiation, according to a team of researchers at Rutgers University.

Americans suffer a million new cases of skin cancer every year, according to the National Cancer Institute.

In mice there is a protective effect from both caffeine and voluntary exercise, and when both are combined the protection is even more than the sum of the two, said Dr. Allan H. Conney of the laboratory for cancer research at Rutgers.

“We think it likely that this will extrapolate to humans, but that has to be tested,” Conney said in a telephone interview.

Nonetheless, he added, people should continue to use sunscreen.

Exposing the mice to ultraviolet-B light causes some skin cells to become precancerous.

Cells with damaged DNA are programmed to self-destruct, a process called apoptosis, but not all do that, and damaged cells can become cancerous.

The researchers report in today’s issue of Proceedings of the National Academy of Sciences that they studied hairless mice in four groups. Some were fed water containing caffeine, some had wheels on which they could run, some had both and a control group had neither.

“The most dramatic and obvious difference between the groups came from the caffeine-drinking runners, a difference that can likely be attributed to some kind of synergy,” Conney said.