Very limited studies had explored the association between depressive symptoms risk and chronic diseases in China. More than 80% of subjects who were with depressive symptoms had chronic diseases. Our findings showed a strong positive association between risk of depressive symptoms and chronic diseases under consideration of socioeconomic confounders.
We found significant associations between depressive symptoms and several socioeconomic factors, such as education attainment, economic level, physical disability and so on. In previous studies, positive associations between gender, age and depressive symptoms were reported [27]. However, we did not observed similar association in the current study. Similar positive association between depressive symptoms and being without spouse or having a lower education level or less wealth was also observed [27]. Low socioeconomic status could make people more likely with depressive symptoms through some mechanisms such as unsafe and unstable environments, malnutrition, reduced possibility of education, and limitedly access to health care services [27].
In the current study, we observed increased risk of depressive symptoms in those with chronic disease, including diabetes mellitus and cerebrovascular disease. The associations between diabetes, hypertension with depressive symptoms were similarly compared with previous studies [19, 20]. These associations could be explained by several mechanisms, including unhealthy lifestyle, shared genetic influences, and inflammation in both diseases [28]. Previous studies also suggested some behavioral or biological pathways that link depressive symptoms risk with diabetes [29]. Furthermore, we found a positive association between depressive symptoms and arthritis after taking socioeconomic factors into consideration. The risk of depressive symptoms of participants with arthritis is 1.72 times as much as those without arthritis. Previous studies suggested that pain and physical disability experience could lead a side effect on their mood [20]. Another explanation is subjects having depressive symptoms might be more sedentary than those without depressive symptoms, which could cause an increased bone resorption and a lowered bone formation [30, 31].
Our study has several strengths, including the large sample size, the population-based design, and adjustment for a wide range of socioeconomic characteristics. Another noticeable strength is that the measure of all physical illnesses took place prior to the CES-D measurement, thus it helped to minimize the risk of reverse causation. However, our study also has several limitations, which should be taken into consideration by future researchers. As a cross-sectional study, we cannot deduce causative pathways between depressive symptoms and chronic diseases; therefore, future longitudinal research is needed to assess the causal relationships between depressive symptoms, chronic diseases and socioeconomic factors. Moreover, the CLASS does not provide sufficient information on lifestyle factors (i.e., weight, height, smoking, alcohol drinking, and so on) that were suggested as risk factor of depressive symptoms, which should be cautioned in future studies.