Chronic, toxic stress like poverty, neglect and physical abuse early in life can have lasting negative impacts, increasing risk of behavioural problems and increased cumulative life stress, says a study.
Early life stress may lead to smaller brain structures, the findings showed.
"We have not really understood why things that happen when you are two, three, four years old stay with you and have a lasting impact," said Seth Pollak, professor of psychology at the University of Wisconsin-Madison in the US.
Yet, early life stress has been tied before to depression, anxiety, heart disease, cancer, and a lack of educational and employment success, Pollak noted.
For the study, the researchers recruited 128 children around age 12 who had experienced either physical abuse, neglect early in life or came from low socioeconomic status households.
They took images of the children's brains, focusing on the hippocampus and amygdala, which are involved in emotion and stress processing. They were compared to similar children from middle-class households who had not been maltreated.
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Children who experienced any of the three types of early life stress had smaller amygdalae - an almond-shape set of neurons located deep in the brain's medial temporal lobe - than children who had not.
Children from low socioeconomic status households and children who had been physically abused also had smaller hippocampal volumes.
Behavioural problems and increased cumulative life stress were also linked to smaller hippocampus and amygdala volumes.
"Why early life stress may lead to smaller brain structures is unknown," Jamie Hanson from Duke University said.
The study appeared in the journal Biological Psychiatry.