Early childhood adversity and HPA axis activity in adulthood:The importance of considering minimal age at exposure

• Healthy adults first exposed to early adversity between the ages of 3 and 7 – an important time window for amygdala development – show greater cortisol awakening response relative to those first exposed to EA before 3 or after 7. • Healthy adults first exposed to early adversity between the ages of 3 and 7 show blunted cortisol reactivity relative to those first exposed to EA before 3 or after 7. • Minimal age at exposure to early adversity better predicts basal and reactive cortisol levels as opposed to the classical accumulation model of early adversity. Early adversity (EA) modulates stress hormone secretion in mixed directions. The Accumulation Model suggests that the number of EA predicts patterns of cortisol dysregulations, while the Life Cycle Model of Stress highlights the importance of considering the timing at which EA began, given that brain regions sensitive to stress hormones follow distinct developmental trajectories. We aimed to test these two models in 85 healthy men and women, aged 21–40 years old who reported having been exposed to EA during childhood. Participants were grouped based on the number of EA events to which they were exposed during their lifespan (Accumulation Model) and the age of first exposure to EA (Life Cycle Model). Diurnal and stress-induced reactive cortisol secretion were measured in all participants. Results showed that although the number of EA was not associated with patterns of basal or reactive cortisol secretion, adults first exposed to EA between the ages of 3 and 7 – an important time window for amygdala development – showed greater cortisol awakening response and lower cortisol reactivity relative to those first exposed to EA before 3 or after 7. These results provide support for the Life Cycle Model of Stress and highlight the importance of considering minimal age at exposure to EA when assessing the effects of early adversity on patterns of cortisol secretion.