Women with dense breast tissue are at higher risk of developing breast cancer, and physical activity has been thought to protect against the disease. But the protective effect of physical activity on breast cancer appears to be through other mechanisms besides reducing breast density, according to data presented at the European Breast Cancer Conference (EBCC), underway in Amsterdam and sponsored by the European Cancer Organization (ECCO).
Shadi Azam of the University of Southern Denmark in Esbjerg and colleagues analyzed the physical activity of more than 5,700 pre- and postmenopausal women who underwent breast cancer screening between 1991 and 2001. Of these women, 56.3% had mixed or dense breast tissue. As for physical activity, 47.5% participated in sports, 70.1% cycled, 52.2% did gardening, and 92.7% walked.
Although Azam's team initially found a significant association between participation in sports and cycling with the chances of having denser breasts, the odds of having dense breasts were reduced and did not reach a statistically significant level after the researchers adjusted for other factors. And the association of reduced cancer risk from physical activity or gardening in women with dense tissue was weak, according to the researchers.
"In the light of our findings, we believe that further studies should now be focused on other mechanisms that might explain the association between physical activity and breast cancer risk," Azam said in a statement released by the ECCO.