Hair cortisol as a risk marker for increased depressive symptoms among older adults during the COVID-19 pandemic

Determining pre-existing biological risk markers of incident depression and other mental health sequelae after exposure to a new stressor would help identify vulnerable individuals and mechanistic pathways. This study investigated primarily whether hair cortisol predicted elevated depressive symptoms in middle-aged and older adults during the COVID-19 pandemic, 6 years later. A secondary aim was to deduce whether any association differed by sex. METHODS: We studied 1025 adults aged 50 and older (75% female) as part of The Irish Longitudinal Study on Ageing. Hair cortisol samples were collected at 2014 (Wave 3) and depressive symptoms were assessed using the 8-item Center for Epidemiological Studies Depression Scale in 2014 (Wave 3), 2016 (Wave 4), 2018 (Wave 5) and again in 2020 as part of TILDA's COVID-19 Study. Hierarchical mixed effects logistic regression models were applied to investigate the association between cortisol levels and clinically significant depressive symptoms before and during the COVID-19 pandemic. RESULTS: In a full covariate adjusted model there was a significant interaction between cortisol and wave on depressive symptoms (χ2 = 8.5, p = .03). Cortisol was positively and significantly associated with elevated depressive symptoms during the COVID-19 Study (OR =1.3, 95% CI 1.11, 1.56, p = .003), and was associated with an increased likelihood of reporting clinically significant depressive symptoms during first year of the COVID-19 pandemic, when compared with before, OR = 1.4, 95% CI 1.05, 1.9, p = .015. There was no evidence of effect modification by sex. CONCLUSIONS: Higher hair cortisol, assessed 6 years previously, predicted clinically significant depressive symptoms among middle-aged and older adults during (but not before) the pandemic. Findings suggest a biological phenotype which denotes increased susceptibility to the negative impact of environmental stress on psychological health.