A recently published theory suggests depression, present today in an estimated 10% of the US adult population, may have helped past generations protect themselves from infection and provided them with an evolutionary edge.
Co-authored by Charles L. Raison, MD, College of Medicine, University of Arizona, and Andrew H. Miller, MD, Emory University School of Medicine, their hypothesis, Pathogen Host Defense (PATHOS-D), is published in the online journal Molecular Psychiatry.
Unlike previous theories on how depression influences behavior in a social context, the authors propose a link between depression and pathogen host defense. They contend that depression, triggered by genetic variations, provided protection from infection, at one time a leading cause of death. Later with the advent of life-saving antibiotics in the early 1900s, people avoided early infectious mortality and passed on their genes.
These genetic variations that support depression occurred during the evolutionary process and helped earlier generations battle infection. The authors say those suffering from depression, long linked to immune system inflammation, often show elevated levels of inflammation without the presence of infection. Miller says the link between the genes and depression affects immune system function, which led the psychiatrists to reexamine why depression appears to remain in the genome.
“Depression and the genes that promote it were very adaptive for helping people, especially young children, not die of infection … even if those same behaviors are not helpful in our relationships with other people,” Raison wrote.
The authors’ hypothesis is not the first to associate depression with defense against infection. They report at least one previous hypothesis has suggested depression as a behavioral response that helps the immune system combat existing infections while avoiding additional pathogen exposure. Their PATHOS-D theory, however, “suggests something qualitatively different and more far-reaching; specifically that depressive symptoms were integral components of immune-mediated host defense against pathogens in the ancestral environment.”
Currently, Miller and Raison are working on research to determine if certain medications used to treat auto-immune diseases can also be useful for treatment-resistant depression.
Disclosure: The researchers report no relevant financial disclosures.