WASHINGTON, June 17 (UPI) -- Low-income children exposed to unstable family environments or insensitive caregiving at age of 2 are at increased risk of cognitive delays by age 4, a new study shows.
While the specific biological or environmental reasons for this are not known, differences in cortisol levels in children in the study at age 2 predicted their cortisol levels as well as cognitive delays at 4.
Researchers followed 201 low-income mother-child pairs in the northeastern United States, assessing the children at ages 2, 3 and 4, surveying their family experiences and collecting cortisol samples.
"We found that children's cortisol levels remained relatively stable across the three years," said Jennifer H. Suor, a doctoral student in clinical psychology at the University of Rochester, in a press release. "And we discovered that exposure to specific forms of family adversity when children were 2 years old predicted their cortisol profile, which in turn was linked with notable differences in children's cognitive functioning at age 4."
About 30 percent of the children had elevated cortisol levels, 40 percent had low cortisol, and the remaining 30 percent had moderate levels of the hormone.
Researchers reported that the children with both higher and lower levels of cortisol had experienced family instability, and that the children with higher cortisol had experienced harsh or insensitive caregiving. Children with both higher and lower levels of cortisol had lower levels of cognitive functioning at age 4.
Children with moderate levels of cortisol experienced relatively less family instability and had the highest cognitive ability at age 4.
"Our study shows that children's cortisol activity and the experience of specific family adversities may be key processes that predict cognitive development for children from low-income backgrounds," said Melissa L. Sturge-Apple, an assistant professor of psychology at the University of Rochester and a member of the research team.
"The exact mechanisms through which too much or too little cortisol affects cognitive functioning aren't fully understood," Sturge-Apple said. "Researchers hypothesize that too much cortisol can have toxic effects on parts of the brain that are important for cognitive functioning, and too little might hinder the body's ability to recruit the biological resources necessary for optimal cognitive functioning."
The study is published in Child Development.