Background: Preclinical studies demonstrate that the neonatal environment can permanently alter an individual's responses to stress. To demonstrate a similar phenomenon in humans, we prospectively examined the relationships of maternal stress beginning in infancy and concurrent stress on preschoolers' hypothalamic-pituitary-adrenal activity and later mental health symptoms.
Methods: Salivary cortisol levels were assessed in 282 4.5-year-old children and 154 of their siblings. Maternal reports of stress were obtained when the children were ages 1, 4, and 12 months, and again at 4.5 years. Children's mental health symptoms were assessed in first grade.
Results: A cross-sectional analysis revealed that preschoolers exposed to high levels of concurrent maternal stress had elevated cortisol levels; however, a longitudinal analysis revealed that concurrently stressed children with elevated cortisol also had a history of high maternal stress exposure in infancy. Importantly, children exposed only to high levels of concurrent or early stress had cortisol levels that did not significantly differ from those never exposed to stress. Further analysis of the components of stress indicated that maternal depression beginning in infancy was the most potent predictor of children's cortisol. We also found that preschoolers with high cortisol levels exhibited greater mental health symptoms in first grade.
Conclusions: These results link the findings of preclinical studies to humans by showing that exposure to early maternal stress may sensitize children's pituitary-adrenal responses to subsequent stress exposure.