Exercise prevents cancer, only with sleep

BETHESDA, Md., Nov. 18 (UPI) -- Regular physical activity can lower a woman's overall risk of cancer but only if she gets a good night's sleep, U.S. researchers said.

Lead author James McClain, a cancer prevention fellow at the National Cancer Institute, said a lack of sleep can undermine exercise's cancer prevention benefits.

"Greater participation in physical activity has consistently been associated with reduced risk of cancer incidence at several sites, including breast and colon cancers," McClain said in a statement. "Short duration sleep appears to have opposing effects of physical activity on several key hormonal and metabolic parameters, which is why we looked at how it affected the exercise/cancer risk relationship."

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

Researchers assessed the association between physical activity energy expenditure, sleep duration and incidence of overall, breast and colon cancer in 5,968 women with no previous cancer diagnoses. The women completed an initial survey in 1998 and were then tracked for nearly 10 years.

McClain presented the findings at the American Association for Cancer Research's Seventh Annual International Conference on Frontiers in Cancer Prevention Research.