Women who have never smoked tobacco, particularly African-Americans, are susceptible to chronic obstructive pulmonary disease (COPD), a disease strongly associated with smoking. Other factors, from hormones to exposure to air pollutants linked to poverty or second-hand smoke, are among the likely reasons for this finding, researchers said.

The study, “COPD in a Population-Based Sample of Never-Smokers: Interactions among Sex, Gender, and Race,” was published online in the International Journal of Chronic Diseases.

The study was conducted by researchers at the University of Toronto, and based a representative sample drawn from the 2012 Behavioral Risk Surveillance of 129,535 Americans, age 50 and older, who had never smoked.

The sample included 8,674 African-American women, 2,708 African-American men, 80,317 white women, and 37,836 white men.

An analysis found that, among these non-smokers, 7% of African-American women have COPD, and 5.2% of white women. Among men, 2.9% of whites had COPD, as did 2.4% of blacks.

“Some of women’s greater vulnerability to COPD may be due to physiological differences. When we took into account height (a proxy for lung size), the odds of COPD among women compared to men were less elevated. However, we still found women had approximately 50% higher odds of COPD compared to white men even when we adjusted for height, education, income, and health care access,” Esme Fuller-Thomson, the study’s lead author and director of the Institute for Life Course & Aging at the University of Toronto, said in a press release.

“Hormones may also play a role. In addition, women are more likely to have been exposed to second-hand smoke from spouses who smoke,” Fuller-Thomson added.

Smoking remains the biggest risk factor for COPD, but other health and environmental factors have been identified as contributors to the onset of the disease as well. Approximately one-quarter of Americans who have been diagnosed with the disease have never smoked.

“African American women had, by far, the highest prevalence of COPD among older adults who had never smoked,” said Rachel Chisholm, a co-author of the study. “We found that after adjusting for income and education levels, the odds of COPD among African American women compared to white men declined by more than half. We cannot determine causality with this data set, but poverty is associated with increased exposure to toxins, such as second-hand smoke in work-places and air pollution in inner city environments. Future research needs to investigate if these factors play a role in the greater vulnerability of African American women.”

The researchers believe that their findings should spur more screening for the disease among those who have never smoked, particularly in the African-American community.

“Primary care physicians and other health professionals should consider screening all their older patients for COPD, including those who have never smoked. Women, particularly African-American women, have an unexpectedly high prevalence of COPD,” Fuller-Thomson said. “Earlier detection of COPD has been found to improve patient outcomes in both the short and long-term and is therefore an important clinical goal.”