Abstract
Both asthma and depression are common conditions that are associated with premature mortality and morbidity. In the literature, there is a consistent positive association between asthma and depression in the general community. However, the health consequences of this association as well as groups at greater risk for this association are not well established. Demographic variables (such as age, gender, race/ethnicity, and poverty), and medical and behavioral risk factors (such as cigarette smoking and obesity) moderate the association between asthma and depressive symptoms. Associations between asthma, depressive symptoms, and inflammation and immunity may also exist. We used existing publically available data from the 2004-2008 National Health and Nutrition Examination Surveys (NHANES) to examine these associations (n=11,329). Asthma was measured by self-report and depression by the 9-item Patient Health Questionnaire. Linear regression was used to test interactions between asthma and several subgroups mentioned above. Structural equation modeling was used to establish associations between asthma, depression, and inflammatory biomarkers. Asthma was positively associated with a total score of depressive symptoms. Overall, there were significant interactions between age and asthma and poverty and asthma on the total score of depressive symptoms, such that the association between asthma and depressive symptoms was stronger for middle aged persons and persons living in or near poverty. Analyses stratified by age (i.e., young, middle aged, and older aged) and poverty (i.e., near poor or poor versus not near poor or poor) revealed interactions by smoking and asthma and body mass index and asthma. Among young persons living in or near poverty, the association between asthma and the total score of depressive symptoms was stronger for current smokers than never smokers. Among young persons not living in or near poverty, middle aged persons living in or near poverty, and older persons not living near or in poverty, the association between asthma and the total score of depressive symptoms was stronger for obese compared to normal weight persons. Structural equation modeling was used to test associations between asthma, depressive typology, and inflammation and immunity. Among middle aged persons living or near poverty, there were significant indirect effects from asthma to the symptoms of somatic depression to the total number of white blood cells, monocytes, and lymphocytes. In summary, results from this study indicated that associations between asthma and depressive symptoms were evident for only select population subgroups. Last, somatic depression is a mediator of the association between asthma and some inflammation indicators among middle aged persons living in or near poverty.