Past studies have shown that exercise offers protection against cancer, and other studies have shown that cutting back on sleep can, among other things, compromise immunity. Until now, no one, however, has looked at the effect of inadequate sleep on the benefits of exercise in reducing cancer risk.

A group of researchers funded by the John Hopkins School of Public Health and led by James McClain, a Cancer Prevention Fellow from the National Cancer Institute, followed almost 6,000 cancer-free women for 10 years. The women reported on their levels of physical activity and sleep through questionnaires.

At the end of the study period, researchers found that exercise reduced cancer risk among the most active women. But this benefit was diminished in younger and more active women who tended to sleep less than seven hours a night. The cancer risk in these women increased by 47 percent compared with women sleeping at least seven hours a night or more. No such relation was observed in older women, and sleep alone did not reduce cancer risk.

“Exercise may reduce cancer risk by improving immunity, regulating insulin and glucose levels, and by maintaining normal sex hormone levels,” said McClain. “Inadequate sleep, on the other hand, might have the opposite effect.” BOTTOM LINE: The benefit of physical activity in reducing cancer risk is diminished by a lack of sleep among younger women. WHAT’S NEXT: Confirm these findings in a larger group of women and try to understand how lack of sleep may be increasing cancer risk. CAUTIONS: This is the first study of its kind and more work is needed to confirm these findings. WHERE TO FIND IT: The study was presented at the American Association for Cancer Research conference on Frontiers in Cancer Prevention and can be found at http://www.aacr.org/home/public–media/news.aspx?d=1191

SENA DESAI GOPAL