Hair cortisol predicts susceptibility to increased depressive symptoms among older women during the COVID-19 pandemic: implications for the vulnerability-stress model of psychopathology

BACKGROUND: Determining pre-existing biological risk markers of incident depression after exposure to a new stressor might help identify vulnerable individuals. We investigated whether hair cortisol predicted increased depressive symptoms during the COVID-19 pandemic, 6 years later. METHODS: We studied 933 older adults as part of The Irish Longitudinal Study on Ageing. Depressive symptoms were assessed before (time 1) and during (time 2) the COVID-19 pandemic, and hair cortisol was measured 6 years previously. Hierarchical mixed effects poisson regression models were applied to investigate the association between cortisol and any change in symptoms. RESULTS: In a fully covariate adjusted model higher cortisol was not associated with depressive symptoms at time 1 (p =.910) but was at time 2 (IRR= 1.05, p=.020), with a significant effect of the cortisol X time interaction (IRR= 1.06, p=.003). Stratified analyses revealed an effect in women only (IRR = 1.07, p=.001). CONCLUSIONS: Higher hair cortisol was associated with increased depressive symptoms among older adults during (but not before) the pandemic. Findings suggest a biological phenotype which denotes increased susceptibility to the negative impact of stress on mental health.