Physical activity and breast cancer risk among Asian‐American women in Los Angeles

BACKGROUND To the authors' knowledge, there have been few studies published to date regarding physical activity patterns and breast cancer risk in Asian and Asian‐American women. METHODS The authors conducted a population‐based case–control study of 501 Asian‐American women with incident breast cancer and a control group of 594 Asian‐American women in Los Angeles County to evaluate the role of lifetime physical activity on breast cancer risk. Information concerning lifetime recreational physical activity (i.e., type of activity, duration [years], and frequency [average hours per week]) and occupational physical activity was obtained using a structured questionnaire that was administered in person. RESULTS Increasing years and levels (average metabolic equivalent [MET] hours per week) of lifetime recreational activity were associated with a significantly reduced risk of breast cancer after adjusting for demographic factors, migration history, and menstrual and reproductive factors. Compared with women who had no lifetime recreational physical activity, ≤ 3 MET hours per week, > 3–6 MET hours per week, > 6–12 MET hours per week, and > 12 MET hours per week of activity were associated with significantly reduced risk, with odds ratios (and 95% confidence intervals) of 0.91 (0.55–1.49), 0.65 (0.39–1.10), 0.53 (0.31–0.90), and 0.47 (0.28–0.80), respectively ( P value for trend < 0.001). The risk of breast cancer was associated inversely with occupational physical activity, although the result was not statistically significant. CONCLUSIONS The findings of the current study provide further support for the finding that physical activity has a protective role in breast cancer. Cancer 2003;10:2565–75. © 2003 American Cancer Society. DOI 10.1002/cncr.11364