Tough experiences before age six, like family instability or abuse, are tied to changes in brain structure and to a higher risk of anxiety or depression, according to a study of mother-son pairs in England.

"Early adversity increases later symptoms of depression or anxiety, which, in turn, can associate with variation in cortical structure," said senior author Edward D. Barker of the Institute of Psychiatry, Psychology, and Neuroscience at King's College London.

"Most children will experience a degree of adversity, but this is not necessarily harmful," Barker told Reuters Health by email. "Our research suggests that children who experience many forms of adversity are at risk."

His team followed almost 500 pairs of mothers and sons, starting during pregnancy, from 1991 or 1992.

When the children were eight, 21, 33, 47, 61 and 73 months old, roughly from infancy to age six, their mothers answered questions about 37 types of  "adversity" in the home, including interpersonal loss, family instability, and abuse toward the child or mother.

When the boys were seven, 10 and 13 years old, their mothers reported on their symptoms of anxiety or depression.

Between age 18 and 21, the young men had magnetic resonance imaging of their brains.

According to the MRI scans, having experienced more types of adversity before age six was tied to lower gray matter volume in an area of the brain called the anterior cingulate cortex, which is involved in emotion, decision-making and empathy, and higher volume in the precuneus, which is involved with episodic memory.

"The relationship is likely similar for girls, but this needs to be confirmed," Barker said.

Early adversity was also tied to lower volume in the right superior frontal gyrus of the brain, as were later symptoms of anxiety and depression, the researchers reported in JAMA Pediatrics.

The right superior frontal gyrus may be related to self-awareness.

Researchers are still learning what processes the precuneus is involved with and how that might be related to problems after early life stress, said Jamie L. Hanson of the Carolina Consortium on Human Development at Duke University who was not part of the new study.

"It can be difficult to know if an effect is a direct result of an experience (like early life stress) or caused by the other effects of an experience (indirect; early life stress is related to depression, and depression can affect the brain)," Hanson told Reuters Health by email. "his study found that differences in the superior frontal gyrus were related to these "indirect" effects."

Child maltreatment, extreme poverty, or having a parent with major mental health issues happens to almost a million kids in the U.S. each year, Hanson said.

"Research suggests that the experiences early in life really matter, especially before the age of five," Hanson said. "This isn't to say that if a child experiences stress during this period, that they will definitely have physical or mental health issues. Stress during infancy and early childhood, however, does increase the risk for many different problems."

"Young children are dependent on their caregivers, whereas teenagers have a greater range of experience and autonomy," Barker said.

Dr. Martin H. Teicher, associate professor of psychiatry at Harvard Medical School in Boston, told Reuters Health that early life adversity plays an important role in risk for substance abuse, personality disorders, anxiety disorders and even psychotic disorders.

"We do not yet know if there are actions that can be taken later in childhood or during adolescence that would preempt the consequences of early exposure," Teicher, who was not part of the study, wrote by email.

Social programs where registered nurses visit low-income first-time mothers have had strong positive effects, Hanson said. "These programs start during pregnancy and typically continue for two years following a child's birth, and really help maternal and child health outcomes."