Changes in hair cortisol among Brazilian adolescents before and during the COVID-19 pandemic

Adolescence is a sensitive developmental period marked by increased reactivity of the HPA axis to environmental stressors. However, little is known about how chronic cortisol levels change during prolonged adversity. Using the COVID-19 pandemic as a natural experiment, this study examines how large-scale environmental disruption affects HPA-axis regulation during adolescence. We investigated hair cortisol concentration (HCC) pre- and during the pandemic in adolescents from Pelotas, Brazil, and identified predictors for change. Data were drawn from the 2004 Pelotas Birth Cohort, a population-based longitudinal study. Hair samples (3 cm) were collected at the 15-year pre-pandemic assessment (T1; 2019–2020) and again at the 17-year mid-pandemic assessment (T2; 2021). HCC was quantified via ELISA method. Socioeconomic, demographic, and pandemic-related experiences, as well as self-reported stress levels, were assessed as potential determinants of changes in HCC. A multivariate latent change score (LCS) model was used to analyze changes in HCC and their associations with predictors. A total of 1,509 individuals were included in the analyses. There was a significant mean increase in HCC of 1.89 pg/mg ( p < 0.001) from T1 to T2. Pandemic-related experiences, such as maternal job loss ( p = 0.005) and higher levels of perceived stress ( p = 0.041), were associated with greater increases in HCC. Government cash transfer program participation ( p < 0.001), having a black or mixed-race mother ( p = 0.017), and being female ( p < 0.001) were associated with lower increases in HCC. Findings suggest significant physiological effects of the COVID-19 pandemic, highlighting the role of demographic, socioeconomic, and pandemic-related factors in shaping cortisol responses and advancing understanding of its impact on adolescent health, with implications for policy and support in low- and middle-income countries. These findings highlight the intricate relationship between cortisol changes and psychological outcomes across various populations during the pandemic.