The etiology of autoimmune disease is still a debate and unclear.
A population-based study including approximately 1.1 million people was conducted using linked Danish registries to investigate the association between depression and the risk of autoimmune disease. The findings show that depression to be associated with a significantly increased risk of autoimmune disease, compared to those without a history of depression. Results suggest a general increased risk of autoimmune diseases following the onset of depression during first, which remained higher for the subsequent 11 years and beyond.
Depression appears to be associated with an increased risk of a range of autoimmune diseases as Type 1 diabetes mellitus, Addison’s, Multiple sclerosis, and Crohn’s disease.
These findings can be explained by the fact that depressive symptoms can have a prolonged impact on neuroendocrine pathways such as the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis. These pathways can both directly and indirectly regulate immune functioning. After continuous stimulation of these connections, the immune system can dysregulate which may lead to the development and progression of autoimmune disease.
The second finding of this study is that depression was more strongly associated with a higher risk of autoimmune diseases characterized as immune Th1-type and/or mixed Th1/Th2-type responses. Cytokines are the hormonal messengers responsible for most of the biological effects in the immune system. Cytokines they are numerous, but can be functionally separated into two groups: 1) those that are proinflammatory Th1 type and 2) those that are essentially anti-inflammatory but that promote allergic responses, Th-2 type.
Examples of Th-1 dominant condition are Hashimoto thyroiditis and Graves’ disease. And for Th-2 dominant condition: Lupus and Allergies.