That's according to the University of Southern California's Veronica Wendy Setiawan, PhD, and colleagues. Their report appears in the October Cancer Epidemiology Biomarkers & Prevention.
They studied data on 739 postmenopausal women in Hawaii and California.
The group included 240 black women, 231 Latinas, 96 Japanese-Americans, 91 whites, and 81 Native Hawaiians.
The women were at least 56 years old and were in their mid- to late 60s, on average.
They completed surveys about their weight, diet, alcohol and tobacco use, exercise, medical history, family cancer history, reproductive history, and hormone use.
The women also provided blood samples. The researchers used those blood samples to measure the women's blood levels of estrogen and other sex hormones.
None of the women was on postmenopausal hormone therapy when their blood was taken.
The researchers tracked breast cancer rates for each ethnic group, adjusting for factors including age, BMI (body mass index), and lifestyle.
Breast Cancer Rates, Hormone Levels
Native Hawaiians had the highest breast cancer rates, followed by Japanese-Americans, whites, blacks, and Latinas.
Blood levels of sex hormones varied among ethnic groups.
Native Hawaiians had the highest sex hormone levels. Blacks and Japanese-Americans had higher estrogen levels than whites. Latinas and whites had similar estrogen levels.
The reasons for those patterns aren't clear.
The study doesn't prove that hormone levels were solely responsible for the groups' breast cancer rates. More studies are needed, the researchers note.
Setiawan and colleagues say their findings add to the sparse data on sex hormone levels in the Latino and Native Hawaiian populations.
SOURCES: Setiawan, V. Cancer Epidemiology Biomarkers & Prevention. October 2006; vol 15: pp 1849-1855. News release, University of Southern California.
By Miranda Hitti
Reviewed by Louise Chang