Depression and asthma—two of the most vexing public health issues in the United States—were once thought to have no connection.
But a new study by School of Public Health researchers at the Slone Epidemiology Center has found evidence that depressive symptoms may be linked to the development of adult-onset asthma in African American women. The likely pathway: stress.
“The hypothesized mechanism linking depressive symptoms to asthma incidence is stress and its physiological consequences—particularly, effects on the immune system and the airways,” says study lead author Patricia Coogan (SPH’87,’96), an SPH research professor of epidemiology. “Psychological stress can bias the immune system to responses that might contribute to asthma.”
In the study, published online earlier this month in the Annals of Allergy, Asthma & Immunology, Coogan and the Slone team followed, between 1999 and 2011, nearly 32,000 African American women—participants in the long-running Black Women’s Health Study—who completed health questionnaires every two years. The researchers rated the frequency with which women experienced 20 depressive symptoms.
Responses such as “I felt depressed,” “I felt lonely,” or “I could not get going” were summed into a scale ranging from zero (rarely or never experiencing depressive symptoms) to 60 (experiencing all depressive symptoms most or all of the time). The scale is commonly used in epidemiologic studies, with a score of 16 or higher used to identify individuals at high risk for depression.
The research team found that as the frequency of depressive symptoms increased, the incidence of adult-onset asthma also rose—up to a twofold increase in women in the highest category of the depressive symptom scale. The incidence of asthma increased 2.8 times in women who had a symptom score of 16 or higher and who also reported use of antidepressants, a group at higher likelihood of suffering from depression.
Coogan says the results were consistent with findings from several previous studies of depression and asthma incidence conducted in smaller and primarily white populations. But, she adds, “I was surprised at the magnitude of the relative risk in our highest category of depressive symptoms.”
According to the investigators, 11.6 percent of black women currently have asthma, and 13.1 percent have a lifetime prevalence of major depressive disorder. When the conditions occur concurrently, both are usually more severe.
Unlike children who experience intermittent asthma symptoms in response to allergy triggers or respiratory infections, adults with newly diagnosed asthma generally have persistent symptoms. Daily medications may be required to keep asthma under control. The condition can be fatal if not properly treated.
About half of adults who have asthma also have allergies. In some cases, adult-onset asthma may be the result of exposure to substances in work or home environments, with symptoms coming on suddenly.
Coogan says that while the new research does not establish a causal relationship between depression and asthma, it does suggest that depressive symptoms can precede asthma—instead of the other way around. The research team ascertained participants’ depressive symptoms before the women developed asthma; those who reported childhood asthma were excluded from the study.
Stress is a known trigger of asthma exacerbation in patients with the condition, Coogan and her colleagues noted in the study. They wrote that a major depressive disorder may lead to overproduction of a corticotropin-releasing hormone and hyperactivity of the hypothalamic-pituitary-adrenal axis—hallmarks of stress.
“This is very early in this research, and speculative,” Coogan warns. “What we can state with certainty now is that there is an association” between depressive symptoms and the onset of adult asthma. “Given the high prevalence of both asthma and depression in women, the association is of public health importance.”
The researchers recommend additional studies exploring the mechanisms by which stress increases asthma risk, in hopes that subgroups at high risk might be identified, generating new therapies for prevention.
The study found a slightly stronger association between depressive symptoms and asthma onset in current and former smokers than in nonsmokers and in women age 40 and older.
In previous research, the Slone team found that experiences of racism or childhood abuse, or having a high body mass index, also were associated with increased incidence of adult-onset asthma. In the case of racism or abuse, the research team hypothesized that those stressful experiences “get into the body somehow,” altering the immune system, Coogan says. And obesity can impact airways and lung function.
While there has been extensive research on childhood asthma, less is known about adult-onset asthma. The next phase of this research by the Slone team is looking into other psychosocial factors in adult asthma, by gauging whether women in economically disadvantaged neighborhoods have higher rates of developing the condition.
The depression link in the Slone study has drawn attention from other researchers interested in the impact of stress on women’s health. “I thought the findings were pretty provocative,” Anna Marsland, a University of Pittsburgh associate professor of psychology and nursing, told Medscape Medical News. “We know about some of the biological pathways that become activated by stress and that those pathways increase vulnerability to lung inflammation and to problems that contribute to symptoms of asthma.”