Two more reasons to exercise, studies find

Mon Dec 11, 4:36 PM ET

CHICAGO (Reuters) - Here are two more reasons to exercise: It may help prevent breast cancer and can be a safer way to lose weight than dieting, doctors said on Monday.
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One report from the Mayo Clinic College of Medicine in Rochester, Minnesota, said a study of women aged 55 to 69 found that those with the highest physical activity levels when the study began had a 14 percent lower risk of developing breast cancer than those who got low levels of exercise.

The multiyear study, which ended in 2003, involved more than 36,000 women.

While the mechanism involved is not clear it may be that exercise reduces body fat, the major source of estrogen in post-menopausal women, the study said. That could lead to fewer tumors of a type called estrogen receptor positive/progesterone receptor negative, which are typically more aggressive, added the report.

"Further studies are needed to confirm these novel findings, and to evaluate similar relationships among premenopausal women," concluded the report published in the Archives of Internal Medicine.

"If found to be causally related to breast cancer, physical activity would have a substantial public health effect on the prevention of this disease, along with its other positive health benefits," it added.

In another study published in the same journal, doctors at Washington University School of Medicine in St. Louis found that people who slim down by cutting calories may also be losing bone density -- something that does not happen if weight loss comes through exercise.

Loss of bone density can lead to osteoporosis and fractures later in life.

That finding was based on a look at 48 adults involved variously in weight loss by caloric restrictions or exercise.

"A common explanation given for the bone loss induced by weight loss is reduction in mechanical stress on the weight-bearing skeleton (the hip and spine)," the report said.

But when muscles pull on bones during exercise it is thought to produce strains in the skeleton that stimulate new bone production, the researchers said.

"These findings have important implications in designing an appropriate weight-loss therapy program in middle-aged adults, particularly in the subset of patients who may already be at increased risk for bone fracture," the study concluded.

http://news.yahoo.com/s/nm/20061211/hl_nm/exercise_benefits_dc_2