Abstract
Results of epidemiologic studies suggest an inverse association between breast cancer risk and physical activity; this is one of the few modifiable breast cancer risk factors identified to date. However, only 2 previous studies assessed the association between physical activity and the extent of mammographically‐detected fibroglandular breast density, a marker of breast cancer risk. Moreover, there has been no study of physical inactivity and percent breast density, nor a study of this relationship in Hispanic women, who are less physically active than non‐Hispanic whites. In the Chicago Breast Health Project, we collected information on sociodemographic, reproductive, medical and lifestyle factors and percent breast density, assessed quantitatively using full‐field digital mammography, from 294 Hispanic women. In our study, we examined the independent associations of hours per day of physical inactivity with percent breast density using multivariate linear regression analysis adjusting for age, education, body mass index, parity, menopausal status, use of hormone replacement therapy and smoking status. Overall, the mean percent breast density was low (i.e., 17.7%) and ranged from 1.9% to 54.6%. There was no difference in percent breast density for women who reported 1.5–3.0 hr of physical inactivity per day compared to women who reported 0–1 hr per day (β = −0.08, p = 0.95), but percent density was marginally significantly higher for women who were reported at least 3.5 hr per day of physical inactivity (β = 3.18, p = 0.056). Results were similar, albeit less statistically significant, in analyses of pre/perimenopausal and postmenopausal women separately. These results support the need for further research investigating the effect of physical activity on breast cancer risk. © 2003 Wiley‐Liss, Inc.