Association between the timing of family socioeconomic deprivation and adolescence hair cortisol among adolescent twins: A study of the genetic and environmental processes involved.

Background: While evidence shows that lower socioeconomic status (SES) is related to dysregulated hair cortisol concentration (HCC), the genetic and environmental processes underlying this association remain understudied.

Objectives: (1) to examine whether childhood and adolescence SES are phenotypically related to late adolescence HCC and to what extent these associations are explained by common underlying genetic factors (2) to estimate whether the genetic and environmental etiology of HCC varies according to SES and the timing of these experiences.

Methods: Participants were 422 twin pairs for whom SES was measured in childhood (ages 0-5 years) and adolescence (age 14 years). Hair cortisol was assessed at age 19.

Results: Additive genetic factors explained 39% of variability in HCC, whereas nonshared environmental factors accounted for the remaining 61%. A significant negative association emerged between HCC and family SES assessed in adolescence (β=-.11,p = .02), which was entirely explained by common underlying environmental influences. We also found evidence of stronger genetic contributions to HCC among youths who lived in more disadvantaged households during childhood in comparison to those from wealthier backgrounds.

Conclusions: This study provides first-time evidence that the association between adolescence SES and HCC is environmentally-explained and that genetic influences underlying HCC are not uniformly distributed across the family SES continuum measured during childhood. These findings may pave the way for a fuller understanding of the impact of early adversity on HPA axis activity.