In a commentary, the authors say that several studies show that small children cared for outside the home, especially in poor quality care and for 30 or more hours per week, have higher levels of cortisol than children at home.
‘Cortisol release is a normal response to stress in mammals facing an emergency and is usually useful. However, sustained cortisol release over hours or days can be harmful.
The authors of the study say that raised cortisol levels are a sign of stress and that the time children spend with their parents is biologically more important than is often realized.
Stress has been associated with children, particularly boys, acting aggressively. Not all children are affected, but an important minority is. Raised cortisol levels are associated with reduced antibody levels and changes in those parts of the brain which are associated with emotional stability.
“Environmental factors interact with genes so that genes can be altered, and once altered by adverse childhood experiences, can pass to future generations. Such epigenetic effects need urgent study”, say the authors.
Sir Denis added: “Future research should explore the links between the care of small children in different settings, their cortisol levels, DNA, and behavior.”