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UNT Insider | August 2012 issue | Researcher finds infant stress levels remain high during sleep training

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Researcher finds infant stress levels remain high during sleep training

From a UNT News Service press release

Wendy Middlemiss

Wendy Middlemiss

When the son of Wendy Middlemiss, associate professor of educational psychology, was a baby, she wondered whether infant sleep training, though hugely popular, was a healthy way to help infants learn to sleep through the night without crying.

She also wondered whether this practice, where parents let infants settle themselves to sleep by not responding to their cries, was detrimental to infants' emotional well-being.

When Middlemiss looked for scientific support for the practice of sleep training, she found none. She began working to determine whether parents should respond to their child's nighttime cries. Her research results were recently published in Early Human Development.

"Infants rely on parents to regulate their emotional states in the first year of life -- needing parents to help them when they are upset. Thus, parental non-responsiveness can be detrimental to infants' learning how to calm themselves down when they are distressed," Middlemiss says. "Parents' support of infants when they are distressed, in part marked by parents' emotional availability, can contribute to better quality sleep, as well as better emotional and social skills."

Working with nurses in New Zealand, she studied infants participating in a hospital-based sleep program. In one of the first infant sleep training studies looking at physiological stress responses in mothers and infants, Middlemiss used saliva test kits to study different stress markers, such as cortisol levels, in both subjects. Her findings indicate that parents might have reason to be concerned with how infants experience sleep training, at least during the initial days of this sleep approach.

"We found that while the practice was successful in helping infants to settle themselves to sleep without crying, infants' physiological stress levels remained very high even when mothers' stress responses were lower," Middlemiss says.

Middlemiss says her research indicates that prolonged maternal non-responsiveness is associated with continued high levels of infant stress, at least during the early days of sleep training. She notes this could be a concern if infants' stress levels continued to remain high, as their physiological stress responses are developing in that first year. Chronic stress can cause infants to develop an overactive stress response system, which can result in later difficulties regulating social and behavior responses. These difficulties can include attention disorders, anti-social behavior and possibly even obesity.

Middlemiss' study also found that during sleep training babies may no longer cry at night even when they are distressed, which results in a disconnect between the baby and mother.

"Nighttime care is largely based on questions of how often infants wake at night and whether they need attention as they fall asleep. A parent often prefers to be present when infants fall asleep, but because this practice can lead to more waking it is often discouraged. It is important to realize that sleep is different in adults than it is in babies," Middlemiss says. "Further, infants whose parents attend to them when they wake often sleep for the same amount of time during the night because they may wake for shorter periods."

Middlemiss suggests helping parents understand that letting infants cry themselves to sleep may be associated with continued stress.

"There are other ways to help infants settle themselves to sleep that are not associated with prolonged periods of crying." Middlemiss says. "These alternatives can include schedule wakings, where parents wake infants before they cry and then help to resettle infants to sleep; or faded comforting, where parents slowly decrease the amount of interaction they have with their infants at bed time but still soothing infants and remaining present should infants cry. This will allow infants to self-settle without the distress associated with sleep training. These are better approaches for parents who would like their infants to settle themselves to sleep."

Douglas A. Granger of Johns Hopkins Center for Interdisciplinary Salivary Bioscience Research, Wendy A. Goldberg of the University of California, Irvine, and UNT graduate student Laura Nathans were co-investigators on the project.

Leslie Wimmer with UNT News Service can be reached at

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August 2012

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