High doses of ultraviolet light damage the DNA in skin cells. Normally, damaged cells commit suicide by a process called apoptosis, so that they do not become cancerous. However, damaged cells that do not undergo apoptosis live to become cancerous. A report from Rutgers University showed that exercise and caffeine help to prevent skin cancer. Researchers divided mice into four groups: 1) inactivity, 2) exercise, 3) caffeine and 4) exercise and caffeine. Then all of the mice were exposed to high doses of ultraviolet B light that damaged their skin cells. Caffeine caused a 95 percent increase in apoptosis, exercise caused a 120 percent increase, and those who both exercised and took caffeine had a 400 percent increase in apoptosis.
Cells in your body have multiple small areas called mitochondria that turn food into energy by knocking hydrogen and electrons from carbohydrates, fats, and proteins. The freed electrons can attach to oxygen to form reactive oxygen species (free radicals) that stick to the DNA of cells to damage them and cause cancer. Exercise teaches your mitochondria to turn food into energy with far fewer free electrons, so there are fewer free radicals to damage cells. Caffeine markedly increases an animal's ability to exercise for longer periods of time. Journal reference