Threats to social safety and neuro-inflammatory mechanisms underlying sexual orientation disparities in depression symptom severity: A prospective cohort study of young adults.

Sexual minority individuals have a markedly elevated risk of depression compared to heterosexuals. We examined early threats to social safety and chronically elevated inflammation as mechanisms contributing to this disparity in depression symptoms, and compared the relative strength of the co-occurrence between chronic inflammation and depression symptoms for sexual minorities versus heterosexuals. To do so, we analyzed data from a prospective cohort of sexual minority and heterosexual young adults (n = 595), recruited from a nationally representative sample, that included assessments of early threats to social safety in the form of adverse childhood interpersonal events, three biomarkers of inflammation (i.e., CRP, IL-6, TNF-α) measured at two time points, and depression symptoms over four years. In pre-registered analyses, we found that sexual minorities experienced more adverse childhood interpersonal events, were more likely to display chronically elevated inflammation, and reported more severe depression symptoms than heterosexuals. Adverse childhood interpersonal events and chronically elevated inflammation explained approximately 23 % of the total effect of the association between sexual orientation and depression symptom severity. Further, there was an increased coupling of chronically elevated inflammation and depression symptoms among sexual minorities compared to heterosexuals. These results provide novel longitudinal, population-based evidence for the role of chronically elevated inflammation in linking threats to social safety during childhood with depression symptom severity in young adulthood, consistent with the primary tenets of the social signal transduction theory of depression. Our study extends this theory to the population level by finding that members of a stigmatized population (i.e., sexual minorities) experience a greater risk of depression because of their greater exposure to adverse childhood interpersonal events and the subsequent link to chronic inflammation, highlighting potential biopsychosocial intervention targets.