title: Depression as sickness behavior? A test of the host defense hypothesis in a high pathogen population.
abstract: Sadness is an emotion universally recognized across cultures, suggesting it plays an important functional role in regulating human behavior. Numerous adaptive explanations of persistent sadness interfering with daily functioning (hereafter "depression") have been proposed, but most do not explain frequent bidirectional associations between depression and greater immune activation. Here we test several predictions of the host defense hypothesis, which posits that depression is part of a broader coordinated evolved response to infection or tissue injury (i.e. "sickness behavior") that promotes energy conservation and reallocation to facilitate immune activation. In a high pathogen population of lean and relatively egalitarian Bolivian forager-horticulturalists, we test whether depression and its symptoms are associated with greater baseline concentration of immune biomarkers reliably associated with depression in Western populations (i.e. tumor necrosis factor alpha [TNF-α], interleukin-1 beta [IL-1β], interleukin-6 [IL-6], and C-reactive protein [CRP]). We also test whether greater pro-inflammatory cytokine responses to ex vivo antigen stimulation are associated with depression and its symptoms, which is expected if depression facilitates immune activation. These predictions are largely supported in a sample of older adult Tsimane (mean±SD age=53.2±11.0, range=34-85, n=649) after adjusting for potential confounders. Emotional, cognitive and somatic symptoms of depression are each associated with greater immune activation, both at baseline and in response to ex vivo stimulation. The association between depression and greater immune activation is therefore not unique to Western populations. While our findings are not predicted by other adaptive hypotheses of depression, they are not incompatible with those hypotheses and future research is necessary to isolate and test competing predictions.
authors.affiliation: Institute for Advanced Study in Toulouse, 21 allée de Brienne, MS 102, 31015 Toulouse Cedex 6, France; Department of Anthropology, MSC 01-1040, 1 University of New Mexico, Albuquerque, NM 87131, USA. Electronic address: jonathan.stieglitz@iast.fr.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Stieglitz
authors.affiliation: Integrative Anthropological Sciences Unit, University of California-Santa Barbara, Santa Barbara, CA 93106, USA. Electronic address: ben.trumble@gmail.com.
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Trumble
authors.affiliation: Department of Anthropology, MSC 01-1040, 1 University of New Mexico, Albuquerque, NM 87131, USA. Electronic address: melissaemerythompson@gmail.com.
authors.forename: Melissa Emery
authors.initials: ME
authors.lastname: Thompson
authors.affiliation: Integrative Anthropological Sciences Unit, University of California-Santa Barbara, Santa Barbara, CA 93106, USA. Electronic address: blackwell@anth.ucsb.edu.
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Blackwell
authors.affiliation: Institute for Advanced Study in Toulouse, 21 allée de Brienne, MS 102, 31015 Toulouse Cedex 6, France; Department of Anthropology, MSC 01-1040, 1 University of New Mexico, Albuquerque, NM 87131, USA. Electronic address: hkaplan@unm.edu.
authors.forename: Hillard
authors.initials: H
authors.lastname: Kaplan
authors.affiliation: Integrative Anthropological Sciences Unit, University of California-Santa Barbara, Santa Barbara, CA 93106, USA. Electronic address: gurven@anth.ucsb.edu.
authors.forename: Michael
authors.initials: M
authors.lastname: Gurven
mesh_terms: D015415:Biomarkers / Q000097:blood; D001838:Bolivia / Q000208:ethnology; D002097:C-Reactive Protein / Q000276:immunology; D016207:Cytokines / Q000097:blood / Q000276:immunology; D003866:Depressive Disorder / Q000208:ethnology / Q000276:immunology* / Q000523:psychology; D005260:Female; D054884:Host-Pathogen Interactions / Q000276:immunology; D006801:Humans; D055809:Illness Behavior; D007155:Immunologic Factors / Q000097:blood / Q000378:metabolism; D008297:Male; D008875:Middle Aged
chemical_list: D015415:Biomarkers; D016207:Cytokines; D007155:Immunologic Factors; D002097:C-Reactive Protein
keywords: Depression; Evolution; Host defense; Immune activation; Sickness behavior; Tsimane