Get your daughters off the couch: Research shows exercise during the teen years -- starting as young as age 12 -- can help protect girls from breast cancer when they're grown.

Middle-age women have long been advised to get active to lower their risk of breast cancer after menopause. What's new: That starting so young pays off, too.

"This really points to the benefit of sustained physical activity from adolescence through the adult years, to get the maximum benefit," said Dr. Graham Colditz of Washington University School of Medicine in St. Louis, the study's lead author.

Researchers tracked nearly 65,000 nurses ages 24 to 42 who enrolled in a major health study. They answered detailed questionnaires about their physical activity dating back to age 12. Within six years of enrolling, 550 had breast cancer diagnosed before menopause. A quarter of all breast cancer is diagnosed at these younger ages, when it's typically more aggressive.

Women who were physically active as teens and young adults were 23 percent less likely to develop premenopausal breast cancer than women who grew up sedentary, researchers report today in the Journal of the National Cancer Institute.

OVER HALF OF AMERICANS ON CHRONIC MEDICINES

For the first time, it appears that more than half of all insured Americans are taking prescription drugs regularly for chronic health problems, a study shows.

The most widely used drugs are those to lower high blood pressure and cholesterol -- problems often linked to heart disease, obesity and diabetes.

The numbers were gathered last year by Medco Health Solutions Inc., which manages prescription benefits for about one in five Americans.

Experts say the data reflect not just worsening public health but better medicines for chronic conditions and more aggressive treatment by doctors. For example, more people are now taking blood pressure and cholesterol-lowering medicines because they need them, said Dr. Daniel W. Jones, president of the American Heart Association.

Also, there is the pharmaceutical industry's relentless advertising. With those factors unlikely to change, doctors say the proportion of Americans on chronic medications can only grow.

ASSOCIATED PRESS