Women have made a good deal of welcome progress in the last several decades, but at least one advance is unwanted: chronic obstructive pulmonary disease (COPD) is on the rise in women in prevalence, morbidity and mortality. By 2000, the number of women dying from COPD surpassed the number of men. But the rising number of cases in women has not been matched by medical understanding of the disease's apparent gender-bias.
"The disease expression of COPD in women is different than in men," says Fernando Martinez, M.D., professor of internal medicine at the University of Michigan and senior author on the review, which appears in the second issue for December of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society. "The main reason that we did this study was to highlight that there really are gender differences in the disease, and that they require additional study."
Dr. Martinez and his colleagues assessed the state of medical and scientific knowledge on gender and COPD and found some consistent patterns. Not only are the manifestations of the disease different in men and women, but the risk factors, symptoms, disease, progression, and even diagnosis, are markedly different between the sexes.
COPD actually comprises what used to be considered two distinct diseases: emphysema, or an abnormality in the lung tissue, and chronic bronchitis, an obstruction of the airways. One of the major gender differences in the manifestation of COPD is that women tend to develop more airway obstruction, whereas men tend to develop a more emphysematic manifestation of the disease. But why that is so is still unclear.
"It may reflect differences in exposures, or [genetic] differences in how males and females manifest damage," said Dr. Martinez. "Or it may have nothing to do with underlying genetic differences that are gender-based."
Women also seem to more prone than men to developing COPD from their exposures to risk factors, such as cigarette smoke and smoke from biomass fuels used for cooking in many developing regions of the world. Ironically, a number of studies have also shown that female smokers have a harder time quitting and remaining tobacco-free than males. Because COPD can develop over decades, a significant portion of current cases can be traced back to a rising smoking epidemic among women that began in the 1950s.
Women may be more susceptible to developing COPD from their exposures, but they also predominate among COPD patients who have never smoked, and may have gender-linked genetic factors that predispose them to developing the disease.
And once sick, women also have different experiences than men. They are less likely to be correctly diagnosed or offered appropriate diagnostic tests for COPD. They report more severe shortness of breath, more anxiety and depression. And according to some studies, they report having a lower quality of life because of their disease.
The fact that COPD differs between men and women is undisputed. But answering questions as to how and why, Dr. Martinez emphasizes, is critical in advancing the medical and scientific understanding of the disease. How do men and women differ in exposures and other risk factors? Are the differences biological or behavioral? How do exposure patterns affect their susceptibility to developing the disease and its manifestation? Why does COPD progress more swiftly in women? Do outcomes differ because of gender bias in diagnosis, physiological differences, or phenotypic differences in their disease?
"Whatever the question, whether it is about the biological nature of the disease or clinical impact of therapeutic studies, you have to have a gender analysis," says Dr. Martinez. "It's an absolutely crucial parameter. Appropriate gender analysis has to be taken into account because it may be instrumental in allowing you to interpret what you're trying to study."