A new study offers more reason not to practice “crying it out” with babies.
Researchers at the University of North Texas monitored the cortisol levels of crying babies and their mothers over five nights when the infants were undergoing sleep training in order to learn to “self-settle.”
The researchers found high levels of cortisol, a stress hormone, in both the mothers and the babies during the times the babies were crying. After several days, the babies learned to go to sleep without crying. Researchers found that during these quiet nights, the mothers no longer had high cortisol levels but the babies’ cortisol levels remained high. They had merely learned to remain quiet while distressed.
The study found:
“On the third day of the program, results showed that infants’ physiological and behavioral responses were dissociated. They no longer expressed behavioral distress during the sleep transition but their cortisol levels were elevated.”
“Although the infants exhibited no behavioural cue that they were experiencing distress at the transition to sleep, they continued to experience high levels of physiological distress, as reflected in their cortisol scores.
“Overall, outward displays of internal stress were extinguished by sleep training. However, given the continued presence of distress, infants were not learning how to internally manage their experiences of stress and discomfort.”
The researchers noted that this was the first time the mothers and babies had not been in sync emotionally. The mothers no longer had high stress levels, not realizing that their babies were still just as upset.