Early life stress (ELS) may become embedded into an individual's stress physiology, changing their hypothalamic-pituitary-adrenal (HPA)-axis in an enduring, trait-like fashion. Cortisol is often utilized to investigate HPA-axis function. However, for "trait" cortisol to be a useful construct, it needs to be internally consistent within measurement occasions and show temporal stability of this reliability. These estimates of physiometrics are rarely tested with biological variables such as cortisol. Identifying reliable and stable individual differences in cortisol may be particularly important when examining questions related to the long-term impact of ELS on HPA-axis function. Using confirmatory factor analysis (CFA) to model latent trait cortisol (LTC) may be a useful statistical approach to capture trait-like indexes of HPA-axis functioning. CFA identifies commonalities among repeated cortisol samples to differentiate characteristic patterns (i.e. a trait) from day-to-day or state variation and measurement error. It is unclear whether LTC estimates are stable prospectively, or if ELS is prospectively associated with LTC. Therefore, we derived LTC factors for 84 adolescent girls (ages 10-17 years) using two-morning salivary cortisol samples, collected sequentially for three days at baseline and again at a one-year follow-up. LTC was internally consistent at both assessments and stable over one year. Greater exposure to ELS was associated with lower LTC over a one-year follow-up. Findings support LTC modeling as a useful strategy to estimate trait-like HPA-axis functioning and suggest that exposure to ELS is associated with lower trait-like cortisol.
Keywords: Latent trait cortisol; adolescent girls; confirmatory factor analysis; early life stress; hypothalamic-pituitary-adrenal axis; saliva cortisol.