Exercise may reduce breast cancer risk

DALLAS, April 25 (UPI) -- U.S. researchers speculate that a regular routine of brisk walking, swimming or bicycling may protect against breast cancer by lowering estrogen levels.

Researchers at the University of Texas Southwestern Medical Center in Dallas say they believe estrogen may deactivate genes in breast tissue that suppress breast-cancer development.

Dr. Yvonne Coyle, a physician who researches the epidemiology of cancer, said when estrogen silences these so-called tumor-suppressor genes by a process called methylation -- which is reversible -- the risk for breast cancer increases.

"So many of the risk factors for breast cancer cannot be modified, such as being a woman, getting older or having a family history," Coyle said in a statement. "However, physical activity may be a modifiable risk factor allowing for breast cancer risk reduction."