WASHINGTON (AP) — Get your daughters off the
couch: New 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-aged 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
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 were diagnosed with breast cancer
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 Wednesday in the Journal
of the National Cancer Institute.
The biggest impact was regular exercise from
ages 12 to 22. "This is not the extreme athlete," Colditz
cautioned.
The women at lowest risk reported doing 3
hours and 15 minutes of running or other vigorous activity a week — or, for the
less athletic, 13 hours a week of walking. Typically, the teens reported more
strenuous exercise while during adulthood, walking was most common.
Why would it help? A big point of exercise in
middle age and beyond is to keep off the pounds. After menopause, fat tissue is a chief source of estrogen.
In youth, however, the theory is that
physical activity itself lowers estrogen levels. Studies of teen athletes show
that very intense exercise can delay onset of menstrual cycles and cause
irregular periods.
The moderate exercise reported in this study
was nowhere near enough for those big changes. But it probably was enough to
cause slight yet still helpful hormone changes, said Dr. Alpa Patel, a cancer prevention specialist at the
American Cancer Society, who praised the new research.
And while the study examined only
premenopausal breast cancer, "it's certainly likely and possible"
that the protection from youthful exercise will last long enough to affect more
common postmenopausal breast cancer, too, Colditz
added.
If you were a bookworm as a teen, it's not
too late, Patel said. Other research on the middle-age benefits of exercise
shows mom should join her daughters for that bike ride or game of tennis or at
least a daily walk around the block.
Many breast cancer risks a woman can't
change: How early she starts menstruating, how late menopause hits, family
history of the disease.
Even though the
exercise benefit is modest, physical activity and body weight are risk factors
that women can control, Patel stressed.
"I'd say you and your daughter are
getting off the couch," she said. "Women who engage in physical
activity not only during adolescence but during adulthood lower their
risk."