If you would like to read the full article here and check the references, please follow the link at the bottom. But, in summary ....
“Our diurnal cortisol data indicate the active treatments did not result in chronically elevated levels over time (ie, values were within normative limits), which is necessary for hypothalamic-pituitary-adrenocortical dysregulation.
This is a crucial point when considering the chain of arguments forming the hypothesis that graduated extinction may lead to problematic emotions and behaviors in later child development.
This hypothesis requires a significant and chronic cortisol elevation resulting from graduated extinction, yet is further disconfirmed by examining our long-term emotional and behavioral findings.
No significant difference in children’s emotions and behaviors could be found between groups 12 months after intervention, with internalizing and externalizing behaviors comparable across groups.
This lack of findings concur with a recent 6-year follow-up assessment of a large randomized controlled trial, where no differences in problematic behaviors and mental health were found between children who received behavioral sleep interventions and those in the control group.
The final argument against using extinction-based methods for infant sleep problems is the potential for insecure child-parent attachment.
No significant differences were found in attachment styles between groups, which suggests a lack of evidence between infants’ sleep and attachment.
For parental stress, mothers in both intervention groups reported less stress than mothers in the control group.
The lack of support for dysfunctional child-parent relationships (ie, disinhibited attachment, child-parent closeness and conflict, global relationship) after behavioral sleep interventions has also been found in a recent 6-year follow-up study.
Altogether, our findings and those of Price et al. are the only studies that now form a preliminary evidence base that suggests brief behavioral sleep treatments may help young children sleep, yet do not lead to later emotional and behavioral problems, or later parent-child insecure attachment.”