The study, published in the journal Child Development, finds cortisol increasing over the day and highest in settings with intrusive or over controlling care providers where the child was frequently moved around, had relatively little free play time and was expected to sit quietly and learn by rote.
Researchers at the University of Minnesota in Minneapolis, Georgetown University in Washington and the Oregon Social Learning Center in Eugene say children with high cortisol levels tended to be, in the case of girls, anxious and vigilant or, in the case of boys, angry and aggressive.
"These findings indicate that the behavior of the care provider is associated with both how well children function at child care, and how much their cortisol is elevated," study leader Megan Gunnar of the University of Minnesota says in a statement.
Gunnar and colleagues measured cortisol levels using saliva for about 150 -- mostly white, largely middle-class -- 3- and 4-year-olds in 110 different family child-care homes.
Swim Week Miami Beach 2014 [PHOTOS]