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Co-Sleeping And Biological Imperatives

By James McKenna, PhD

Why Human Babies Do Not and Should Not Sleep Alone

Where a baby sleeps is not as simple as current medical discourse and recommendations against co-sleeping in some western societies want it to be. And there is good reason why. I write to explain why the pediatric recommendations on forms of co-sleeping, such as bed-sharing, will and should remain mixed. I will also address why most new parents practice intermittent bed-sharing despite governmental and medical warnings against it.

Definitions are important here. The term co-sleeping refers to any situation in which a committed adult caregiver, usually the mother, sleeps within close enough proximity to her infant so that each can respond to each other’s sensory signals and cues. Room-sharing is a form of co-sleeping, always considered safe, and always considered protective. But it is not the room itself that is protective. It is what goes on between the mother (or father) and the infant that is. Medical authorities seem to forget this fact. This form of co-sleeping is not controversial and is recommended by all.

Unfortunately, the terms co-sleeping, bed-sharing, and a well-known-to-be-dangerous form of co-sleeping, couch or sofa co-sleeping, are mostly used interchangeably by medical authorities, even though these terms need to be kept separate. It is absolutely wrong to say, for example, that “co-sleeping is dangerous” when room-sharing is a form of co-sleeping, and this form of co-sleeping (as at least three epidemiological studies show) reduces an infant’s chances of dying by one half.

Bed-sharing is another form of co-sleeping that can be made either safe or unsafe, but it is not intrinsically one or the other. Couch or sofa co-sleeping is, however, intrinsically dangerous. Babies can and do all too easily get pushed against the back of the couch by the adult, or flipped facedown in the pillows, and suffocate.

Often news stories talk about “another baby dying while co-sleeping,” but they fail to distinguish between what type of co-sleeping was involved and, worse, what specific dangerous factor might have actually been responsible for the baby dying. A specific example is whether the infant was sleeping prone next to his parent, which is an independent risk factor for death regardless of where the infant was sleeping. Such reports inappropriately suggest that all types of co-sleeping are the same (and dangerous), that all the practices around co-sleeping carry the same high risks, and that no co-sleeping environment can be made safe.

Nothing can be further from the truth. This is akin to suggesting that because some parents drive drunk with their infants in their cars, unstrapped into car seats, and because some of these babies die in car accidents that nobody can drive with babies in their cars because obviously car transportation for infants is fatal. You see the point.

One of the most important reasons why bed-sharing occurs, and the reason why simple declarations against it will not eradicate it, is because sleeping next to one’s baby is biologically appropriate, unlike placing infants prone to sleep or putting an infant in a room to sleep by herself. This is particularly so when bed-sharing is associated with breastfeeding.

When done safely, mother-infant co-sleeping saves infants’ lives and contributes to infant and maternal health and well-being. Merely having an infant sleeping in a room with a committed adult caregiver (co-sleeping) halves the chances of an infant dying from sudden infant death syndrome (SIDS) or from an accident.

Proven by Research

In Japan where co-sleeping and breastfeeding (in the absence of maternal smoking) is the cultural norm, rates of SIDS are the lowest in the world. For breastfeeding mothers, bed-sharing makes breastfeeding much easier to manage and practically doubles the amount of breastfeeding sessions while permitting both mothers and infants to spend more time asleep. The increased exposure to mother’s antibodies that comes with more frequent nighttime breastfeeding can potentially reduce illness for any given infant. And because bed-sharing makes breastfeeding easier for mothers, it encourages them to breastfeed for a greater number of months, according to Dr. Helen Ball’s studies at the University of Durham, therein potentially reducing the mother’s chances of breast cancer. Indeed, the benefits of co-sleeping help explain why simply telling parents never to sleep with baby is like suggesting that nobody should eat fats and sugars since excessive fats and sugars lead to obesity and/or death from heart disease, diabetes, or cancer. Obviously, there’s a whole lot more to the story.

An expanded version of bed-sharing’s function and effects on the infant’s biology helps us to understand not only why the bed-sharing debate refuses to go away, but why the overwhelming majority of parents in the United States (over 50 percent, according to the most recent national survey) now sleep in bed for part or all of the night with their babies.

That the highest rates of bed-sharing worldwide occur alongside the lowest rates of infant mortality, including SIDS rates, is a point worth returning to. It is an important beginning point for understanding the complexities involved in explaining why outcomes related to bed-sharing—recall, one of many types of co-sleeping—vary between being protective for some populations and dangerous for others. It suggests that whether or not babies should bed-share and what the outcome will be may depend on who is involved, under what condition it occurs, how it is practiced, and the quality of the relationship brought to the bed to share. This is not the answer some medical authorities are looking for, but it certainly resonates with parents, and it is substantiated by scores of studies.

Our Biological Imperatives

My support of bed-sharing when practiced safely stems from my research knowledge of how and why it occurs, what it means to mothers, and how it functions biologically. Like human taste buds, which reward us for eating what’s overwhelmingly critical for survival—i.e. fats and sugars— a consideration of human infant and parental biology and psychology reveal the existence of powerful physiological and social factors that promote maternal motivations to cosleep and explain parental needs to touch and sleep close to their baby.

The low-calorie composition of human breast milk (exquisitely adjusted for the human infants’ undeveloped gut) requires frequent nighttime feeds, and therefore helps explain how and why a cultural shift toward increased co-sleeping behavior is underway. Approximately 73 percent of U.S. mothers leave the hospital breastfeeding, and even mothers who never intended to bed-share soon discover how much easier breastfeeding is and how much more satisfied they feel with baby sleeping alongside them in their bed.

But it’s not just breastfeeding that promotes bedsharing. Infants usually have something to say about it too, and for some reason they remain unimpressed with declarations as to how dangerous sleeping next to mother can be. Instead, irrepressible (ancient) neurologically based infant responses to maternal smells, movements, and touch altogether reduce infant crying while positively regulating infant breathing, body temperature, absorption of calories, stress hormone levels, immune status, and oxygenation. In short, and as mentioned above, co-sleeping (whether on the same surface or not) facilitates positive clinical changes including more infant sleep and seems to make, well, babies happy. In other words, unless practiced dangerously, sleeping next to mother is good for infants. The reason why it occurs is because…it is supposed to.

Recall that despite dramatic cultural and technological changes in the industrialized West, human infants are still born the most neurologically immature primate of all, with only 25 percent of their brain volume. This represents a uniquely human characteristic that could only develop biologically (indeed, is only possible) alongside mother’s continuous contact and proximity—as mother’s body proves still to be the only environment to which the infant is truly adapted, for which even modern western technology has yet to produce a substitute.

Even here in the U.S., nothing a baby can or cannot do makes sense except in light of the mother’s body, a biological reality apparently dismissed by those that argue against any and all bed-sharing and what they call co-sleeping, but which likely explains why most crib-using parents at some point feel the need to bring their babies to bed with them—findings that our mother-baby sleep laboratory here at Notre Dame has helped document scientifically. Given a choice, it seems human babies strongly prefer their mother’s body to solitary contact with inert cotton-lined mattresses. In turn, mothers seem to notice and succumb to their infant’s preferences.

There is no doubt that bed-sharing should be avoided in particular circumstances and can be practiced dangerously. While each single bed-sharing death is tragic, such deaths are no more indictments about all bed-sharing than are the 300,000+ deaths of babies in cribs an indictment that crib sleeping is deadly and should be eliminated. Just as unsafe cribs and unsafe ways to use cribs can be eliminated, so, too, can parents be educated to minimize bed-sharing risks.

We still do not know what causes SIDS. But fortunately, the primary factors that increase risk are now widely known—such as placing an infant facedown for sleep, using soft mattresses, maternal smoking, overwrapping babies, or blocking air movement around their faces.

Whether involving cribs or adult beds, risky sleep practices leading to infant deaths are more likely to occur when parents lack access to safety information, or if they are judged to be irresponsible should they choose to follow their own and their infants’ biological predilections to bed-share, or if public health messages are held back on brochures and replaced by simplistic and inappropriate warnings saying “just never do it.” Such recommendations misrepresent the true function and biological significance of the behaviors, and the critical extent to which dangerous practices can be modified, and they dismiss the valid reasons why people engage in the behavior in the first place.