• Science

How Cuddling Saves Tiny Babies

6 minute read

Babies are less obvious creatures than they seem. Yes, their list of demands is short and straightforward: they need food, sleep and frequent diaper changes. And they make their wishes known in an equally direct way—with an ear-splitting wail that is as hard to bear as it is impossible to ignore.

But then, too, there is the need to be cuddled. Eating and sleeping are non-negotiable activities if you want to stay live, and a wet diaper can be impossibly uncomfortable. Unless a baby is cold, however, cuddling ought to be optional—something that happens when a caregiver has time, perhaps, and when the baby is bored or fussy. But that’s not how things work. Babies want, even crave the experience of being held, and adults are generally thrilled to oblige. Now, a study on premature infants, published in the journal Biological Psychiatry, sheds new light on the reason our species is so powerfully wired for cuddles—and provides new insight into the best ways to care for preemies themselves.

It’s no secret that what doctors and parents are increasingly referring to as kangaroo care (KC)—or the simple business of holding babies as much as possible as opposed to leaving them in their cribs or playpens—can have real developmental benefits. Babies who get constant cuddling tend to sleep better, manage stress more easily and exhibit better autonomic functions, such as heart rate. But since you can hardly run a long-term experiment in which you instruct one set of parents to hold their infants and another to let theirs mind themselves, there’s never been any way to measure these benefits accurately. Nearly 18 years ago, however, Ruth Feldman, a professor of psychology and neuroscience at Bar-Ilan university in Tel Aviv, thought she might have a solution.

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Though kangaroo care is standard treatment in neonatal intensive care units (NICUs) today—at least for babies who can spend time outside of incubators—in the 1990s, it wasn’t. Most hospitals felt the risk of exposing preemies and other frail newborns to germs outweighed the undocumented benefits of holding them. In 1996, Feldman assembled two sample groups of 73 babies each at two different Israeli hospitals. One group got standard treatment, which meant no KC; at the other, the mothers would hold their preemies for one hour per day for 14 days. The babies had an average gestational age of 30 weeks—meaning they were ten weeks premature—and an average weight of 2.8 lbs. (1,270 gm).

“Today,” Feldman says, “withholding KC from one group of preemies would be an ethical issue. Back then, though, the benefits weren’t proven, so we just asked one hospital if we could introduce it there.”

Feldman and her team ran the study twice—once in 1996 and again in 1998—switching which hospital did and didn’t provide the kangaroo care, in order to neutralize that as a variable. Then they followed all the babies, examining them when they were 3, 6, 12 and 24 months old, and again when they were 5 and 10 years old. On the whole, she found, the kids in the KC group were outperforming the other group in a range of ways. As babies, they had more-organized—or predictable—sleep patterns; steadier respiration and heart rates; and better affective attention—or the ability to direct their gaze and actions toward a goal. All of those benefits were still in evidence a decade later. The 10 year olds who had gotten KC also showed better stress management, as determined by levels of cortisol—a stress-related hormone—in their saliva when they were faced with an anxiety-producing situation such as delivering a presentation at school.

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“Every mammal has to be cuddled and in close proximity with its mother in the first days and weeks of life,” says Feldman. “This builds up the bodily systems that are sensitive to a physical presence.” In human preemies, Feldman says, the need is especially acute. “We think of prematurity as a proxy for maternal denial, since babies are outside the womb and away from their mothers for months.”

Perhaps the most remarkable thing about Feldman’s findings is just how little KC—14 total hours over 14 days—it took to produce such profound effects. She and her colleagues suggest a range of mechanisms that can explain those results.

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Oxytocin—the feel-good, bonding hormone—increases in both mothers and babies during cuddle sessions, and it is likely to rise similarly in breast milk too, giving babies an additional boost every time they nurse. What’s more, most of the systems that are improved by KC are those that toggle back and forth between what’s known as excitation and inhibition—sleep versus wakefulness, accelerated versus steady heartbeat, stress versus calm. All of those systems are also ones that can be settled by physical contact. Once babies feel what that regulating process is like, they learn to do it on their own. “During sensitive periods in the maturation [of] certain skills,” the researchers write, “even small inputs have major effects.”

Feldman remains in touch with most of her sample group and wants to follow them at least until they turn 17, when she hopes to conduct scans of their brains and see if she can detect lasting effects of the long-ago cuddling there too. In most NICUs in the developed world, neither those results nor the ones in the current paper will change standard practice much, since kangaroo care is already recommended. For those places that don’t yet practice it, however, the new work is a powerful argument for starting. And for parents of healthy, full-term infants, that wisdom holds too. Simply by reaching to be picked up, babies have always let us know what they need the most. Now we know why.

(MORE: New—and Hopefully Improved—Definition of ‘Term Pregnancy’)

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Write to Jeffrey Kluger at jeffrey.kluger@time.com