Contrary to a long-held theory, obesity may not increase the risk of breast cancer among older African-American women, according to research performed at Boston University and at Howard University in Washington, D.C.
The study confirmed the findings of previous studies showing that younger women with a high body mass index (BMI, a weight-height ratio) have a reduced risk of breast cancer. The findings were presented at the annual meeting of the American Association for Cancer Research.
The research team focused on the relationship between breast cancer and various measures of obesity in African-American women in particular because the prevalence of obesity in the U.S. is highest in the African-American population.
The primary data source used was the Black Women's Health study, which enrolled 59,000 participants in 1995 and followed up on the health and medical status of each woman every two years.
After eight years of follow-up, 809 women reported having breast cancer; about half of them were premenopausal and half were postmenopausal at the time of diagnosis. Whether a breast cancer occurs before or after menopause is an important consideration in light of the association between estrogen-fueled proliferation of breast cells and the development and progression of breast cancer.
"Some previous research, but not all, has shown that high body mass index among older women increases breast cancer risk," the researchers explained. "We actually found the opposite in our study. African-American women with a BMI that qualifies them as obese did not have a higher risk of getting breast cancer. In fact, the risk was slightly lower in obese women overall, which is in agreement with findings from another study of black women."
One possible explanation for the discrepancy between the findings for black and white women has to do with differences in when a woman puts on the extra pounds. Black women, in general, become overweight at younger ages than white women.
There is some evidence that the adverse effect of being overweight on postmenopausal breast cancer risk is strongest in the decade right after the weight gain. In this study, no increased risk was associated with current BMI overall, but there was an association between increasing risk and increasing BMI among postmenopausal women under age 50.
The latest report from the American Cancer Society states that the overall rate of breast cancer is 17 percent lower in African-American women than in white women, and the five-year survival rate is 14 percent higher among black women. The researchers point out that their research does not change the message that maintaining a healthy weight is best for overall health.
I have no doubt the weight-breast cancer relationship will be the focus of more research in an effort to better understand the differences in occurrence rates, stage of disease at diagnosis, and prognostic differences among women of different racial and ethnic backgrounds.
