LAUSR

ABSTRACT Stress system activity in early life can have long‐term effects on neurodevelopment. The main aim of this study was to assess the association of child evening salivary cortisol and alpha‐amylase basal levels at 14 months of age with longer‐term neuropsychological development at 4 years in a low‐risk population‐based birth cohort derived from the INMA (Environment and Childhood) project in Spain. We included 186 parent‐children pairs with information on both stress system activity and neurodevelopment. Both stress markers at 14 months of age showed an association with neuropsychological development at 4 years. Salivary cortisol showed a sex‐specific pattern of association. In girls, cortisol levels at 14 months were negatively associated with cognitive development [long‐term declarative memory (&bgr; = − 17.8, p = 0.028; 95% CI = − 33.2 to − 2.5); executive function (&bgr; = − 9.8, p = 0.08; 95% CI = − 21 to 1)] and gross motor development (&bgr; = − 13; p = 0.022; 95% CI = − 24 to − 2), whereas in boys cortisol levels were negatively associated with socioemotional development [autistic‐like behaviours: Incidence Rate Ratio (IRR) = 1.6, p = 0.039; 95% CI = 1.01 to 2.41]. Salivary alpha‐amylase was positively associated with socioemotional development in boys only [social competence (&bgr; = 2.11, p = 0.013; 95% CI = 0.47 to 3.72), autistic‐like behaviours (IRR = 0.93, p = 0.042; 95% CI = 0.87 to 0.99) and hyperactivity symptoms (IRR = 0.81, p = 0.021; 95% CI = 0.69 to 0.97)]. These results suggest that stress system activity in early life is associated with longer‐term neurodevelopment and that sex is an important factor in this relationship.