A study presented at the American Association for Cancer Research’s Seventh Annual International Conference on Frontiers in Cancer Prevention Research has shown that physical exercise decreases cancer risk, but only if it’s accompanied by sufficient nightly sleep.

The study looked at 5,968 women at least 18 years old with no previous cancer diagnoses.

The results revealed that women in the upper 50 percent of physical activity energy expenditure showed significantly reduced risk of overall cancer and breast cancer. However, sleeping less than seven hours a day increased overall cancer risk, negating much of the protective effects of physical activity on cancer risk for this group.

Even though the exact mechanism of how exercise reduces cancer risk isn’t known, researchers believe that physical activity’s effects on factors including hormone levels, immune function, and body weight may play an important role.

Thanks to Eurekalert! for the info.