While it’s still a mystery why African-American women fighting breast cancer have lower five-year survival rates than their white counterparts, one reason can be ruled out: obesity, according to a study published in the Journal of Clinical Oncology and reported by Reuters Health.

To examine this link, researchers from City of Hope, a comprehensive cancer center in Duarte, California, looked at data collected for an earlier breast cancer study. That study included more than 4,500 women living in major American cities. About a third of the participants were black; the rest white. All the women received their cancer diagnosis between ages 35 and 64. But about twice as many black participants were obese, 27 percent versus 12 percent.

At the end of an eight-year period, findings showed 25 percent of the black women had died of breast cancer, compared with 14 percent of white women.

But what scientists found interesting was that obese white women had a 46 percent higher chance of dying of breast cancer compared with their normal-weight peers, and that risk remained even after controlling for other factors. No such link existed for black women.

“It was surprising that this study shows a positive relationship between obesity and breast cancer mortality in white women and not in black women,” said lead study author Yani Lu, PhD, a City of Hope research fellow. “It raises important questions about other possible reasons.”

Researchers did find a small link between extra pounds and cancer death in black women with advanced disease but explained that the link needed support from studies of other groups.

So what could be causing the increase? Some studies found tumor biology and health care access could be factors. For example, previous research showed African-American and Hispanic women aren’t as quick as white women to get drug treatment after breast cancer surgery. In addition, previous research also found that more black women were diagnosed with late-stage breast cancer than white women.

But researchers want people to be clear on how to interpret these study findings. Even though the obesity link wasn’t proved, that doesn’t mean breast cancer survivors should not be concerned about packing on pounds.

Advised Lu, “It’s always important to maintain a healthy weight, for a variety of reasons.”

To learn more about how breast cancer affects the black community, click here.