Exercise improves your health, but can you kill yourself with too much snow shoveling, yard work, jogging, or playing tennis?

"Despite all of the known benefits of exercise, there are also well-documented associations between acute episodes of exertion and sudden cardiac death," notes Christine Albert, an assistant professor of medicine at Harvard Medical School. "Although relatively rare, these deaths commonly occur in an unexpected fashion among those who appear quite healthy."

Leaner women and those who maintain a healthy weight after diagnosis live longer.

The study included 5,204 women with invasive breast cancer who were between the ages 30 to 55 when enrolled in the study in 1976. The researchers found that women who weighed more before they were diagnosed with breast cancer and those who were lean but gained weight after diagnosis and treatment tended to have worse survival outcomes. Intriguingly, the association was strongest in women who did not smoke.