Release Date: February 21, 2003
BUFFALO, N.Y. -- Women who take part in strenuous leisure-time activities vigorous enough to work up a sweat appear to cut their risk of developing breast cancer, researchers at the University at Buffalo have shown.
The study asked women between the ages of 40 and 85 how much physical activity they took part in at 2, 10 and 20 years prior to the interview and at age 16.
Findings showed the strongest protective effect from strenuous exercise at a point 20 years in the past. All women who reported an average of 3.5 hours per week of sweat-producing physical activity at that point in their lives cut their risk of developing breast cancer later in life in half.
Being active in their teens also appeared to be protective. Strenuous activity at age 16 produced a 35-45 percent reduction in risk, findings showed.
The study appears in the February issue of Medicine and Science in Sports and Exercise.
"This is one more small piece of a really large puzzle concerning what protects against breast cancer," said lead author Joan Dorn, Ph.D., assistant professor of social and preventive medicine in UB's School of Public Health and Health Professions.
"To date, few factors related to breast cancer have emerged as being strongly protective, particularly factors that women can modify, so even a modest effect is important."
Physical activity has received much attention recently as a lifestyle component that could offer some potential protection against breast cancer, but study results remain mixed and some research indicated different effects for pre- and postmenopausal women, Dorn said. In addition, researchers have been interested in determining if physical activity at any particular point in a woman's life was particularly protective, she noted.
To attempt to answer these questions, Dorn and colleagues turned to UB's Western New York Diet Study, a population-based, case-control study of newly diagnosed breast cancer patients and randomly selected healthy women in Western New York conducted from 1986-91. One of the study's aims was to examine the association between lifetime physical activity and breast-cancer risk.
The study group consisted of 301 menopausal women and 439 postmenopausal women with breast cancer, and 316 premenopausal and 494 postmenopausal controls. During the initial interview women were asked to report on time spent per week in physical activity strenuous enough to make them sweat at four points (2, 10, and 20 years in the past and at age 16) in their lives. From this information, Dorn and colleagues calculated an average hours-per-week of exercise for each participant at those four points in her life.
Looking at each time period separately, results showed generally a modest protective effect of exercise for both pre- and postmenopausal women who were active at any one time period, Dorn said. Postmenopausal women who were active at all four time periods had a 50 percent decrease in risk, but this protective effect didn't show up for the younger women in the study for reasons that weren't immediately clear, she noted.
However, being active at age 16 and at a point 20 years in the past appeared to be particularly significant. Dorn speculated that these time points may have coincided with significant physiological events in the women's lives.
"The age of menarche and age at first birth have been identified as potentially important periods in the life history of breast cancer," she said. "For the premenopausal women, whose mean age was 46 at the time of the interview, 20 years prior may have placed them, on average, around the time of first pregnancy. It's possible that our observation of a protective effect coincides with this important time period.
"Twenty years post-interview for the postmenopausal women would put them around their mid-40s, when many would be approaching menopause," Dorn noted.
"It's possible that strenuous exercise during this period of a woman's life has an impact on breast cancer by favorably affecting a hormonal milieu in the process of change.
"These results, combined with what we know about the benefits of physical activity in protecting against other chronic diseases, are enough to tell women to get out there and get some exercise," she said.
Additional authors on the study, all from the UB Department of Social and Preventive Medicine, School of Health and Health Professions, were John Vena, Ph.D.; John Brasure; Jo Freudenheim, Ph.D., and Saxon Graham, Ph.D.