NEW YORK (Reuters Health) - Premenopausal women who spend much of their leisure time in physical activities, especially during adolescence and early adulthood, are less likely to develop breast cancer than their more sedentary counterparts, according to a report in the Journal of the National Cancer Institute.
Prior research has linked physical activity with a reduced risk of breast cancer in postmenopausal women, but whether this also applies to younger premenopausal women was unclear, lead author Dr. Sonia S. Maruti, from the Fred Hutchinson Cancer Research Center in Seattle, and colleagues explain.
To address this question, the researchers determined whether physical activity at a particular age or intensity were needed to a see a reduction in risk. The analysis involved 64,777 premenopausal women enrolled in the Nurses' Health Study II who were surveyed regarding leisure-time physical activity from age 12 to their current age.
Overall, 550 subjects developed breast cancer after 6 years of follow-up, the report indicates.
Physical activity was inversely associated with breast cancer risk, the authors found. The strongest association was with total leisure-time physical activity rather than with activity during a certain age period or of a particular intensity. Still, activity between 12 and 22 years of age contributed most to the reduction in risk.
The investigators found that the amount of activity needed to a achieve a 23-percent reduction in risk was roughly equivalent to 3.25 hours of running or 13 hours of walking per week, the report shows.
In women with the highest level of physical activity, the rate of breast cancer was 136 cases per 100,000 persons per year, while in the young women with the activity lowest level, the rate of breast cancer was 194 cases per 100,000 persons per year.
"These results suggest that consistent physical activity during a woman's lifetime is associated with decreased breast cancer risk," the authors conclude. "This association, if found to be causal, has public health implications for prevention."
SOURCE: Journal of the National Cancer Institute, May 21, 2008.
