Still Useful (And Important) After All These Years
Mothers and infants sleeping side by side, also known as co-sleeping, is the evolved context of human infant sleep development. Until very recent times, for all human beings, co-sleeping constituted a prerequisite for infant survival. For the majority of contemporary people outside of the Western industrialized context, it still does. Because the human infant’s body continues to be adapted only to the mother’s body, co-sleeping with nighttime breastfeeding remains clinically significant and potentially lifesaving.
Moreover, since the content of human milk is relatively low in fat and protein and high in sugar, which is metabolized quickly, and since human infants are unable to locomote on their own, continuous contact and carrying, with frequent breastfeeding day and night, is required. Thus, any biological scientific study that attempts to understand “normal,” species-wide, human infant sleep patterns without considering the vital role of nighttime contact in the form of breastfeeding and maternal proximity must be considered inadequate, misleading, and/or fundamentally flawed.2This is because, of all mammals, humans are born the least neurologically mature (25% of adult brain volume), develop the most slowly, and are the most dependent for the longest period of time for nutritional, social, and emotional support, as well as for transportation. Indeed, in the early phases of human infancy, social care is synonymous with physiological regulation. That is, holding, carrying, and/or caressing an infant, and emitting odors and breath in his or her proximity, induce increased body temperature, less crying, greater heart-rate variability, fewer apneas, lower stress levels, increased glucose storage, and greater daily growth.1
Co-sleeping: The Importance of Taxonomic Distinctions
Much of the controversy surrounding the question of the safety of mother– infant co-sleeping involves the ways in which investigators define and conceptualize it. Co-sleeping is not, as the Consumer Product Safety Commission (CPSC) assumes, a single, coherent practice. Rather, it is best thought of as a generic, diverse class of sleeping arrangements composed of many different practices, each of which requires proper description and characterization before the issue of safety and clinical outcomes can be understood.
A safe co-sleeping environment must provide the infant with the opportunity to sense and respond to the caregiver’s signals and cues, such as the mother’s smells, breathing sounds and movements, infant-directed speech, invitations to breastfeed, touches, and any hidden sensory stimuli, whether intended or not.3 Moreover, to be designated as safe, the physical and social co-sleeping environment must involve a willing and active caregiver who chooses to co-sleep specifically to nurture, feed, or be close to the infant in order to monitor or protect him or her.
The co-sleeping environment also must be carefully constructed to avoid known hazardous conditions, recently revealed by epidemiological studies.4 Dangerous types of co-sleeping include sleeping with infants on sofas or couches, bed-sharing with mothers who smoke, and positioning toddlers next to infants. Parents or caregivers desensitized by drugs or alcohol create an unsafe co-sleeping environment. Other dangerous co-sleeping environments occur when an infant sleeps with a larger person on a soft mattress or is placed on large pillows in a bed with a parent.5,6,7
While all forms of bed-sharing are examples of co-sleeping, bed-sharing is only one of perhaps hundreds of different ways to co-sleep practiced around the world. For example, some parents in Latin America, the Philippines, and Vietnam sleep with their infant in a hammock, or place the infant in a hammock to sleep next to them, while they sleep on mats or beds. Some parents place their infant in a wicker basket and put the basket on a bed, between the parents. Other parents sleep next to their infants on bamboo or straw mats or on futons (as in Japan). Some place their infant on a cradleboard, keeping the infant within arm’s reach; others co-sleep by room-sharing, having the infant sleep on a different surface, such as in a crib or bassinet, which is kept next to the parental bed, within arm’s reach.
Co-sleeping Has Not Outlived Its Biological Usefulness
Although forms of infant sleeping vary enormously from culture to culture, the potentially beneficial physiological regulatory effects of maternal contact on human infants during sleep do not. Up to one degree of temperature can be lost when a newborn human is removed from the mother’s stomach following birth, even when the infant is placed in an incubator with ambient temperatures set to match the mother’s body temperature.8 Richard found that among 11- to 16-week-old infants, solitary-sleeping infants exhibited lower average axillary skin temperatures than breastfeeding infants sharing a bed with their mothers.9 Thoman and Graham discovered that even mechanical breathing teddy bears placed next to apnea-prone human newborns have the effect of reducing apneas by as much as 60%, in addition to physically drawing the infant subjects to sleep in direct contact.10 Moreover, when resting on their mothers’ (or fathers’) chests, skin-to-skin, both premature and full-term infants breathe more regularly, use energy more efficiently, grow faster, and experience less stress.11,12,13
Clinical Outcomes Depend on How Co-sleeping Is Practiced
Exactly how co-sleeping may be beneficial or dangerous to the infant varies as a function of the particular social and physical environment (family circumstances) that it is practiced in. This is why there is no single outcome associated with forms of co-sleeping, especially in urban Western cultures, and why there is so much debate about whether co-sleeping, especially in the form of bed-sharing, is safe.
For example, in industrialized urban societies, among middle- to upperclass families where bed-sharing and breastfeeding are practiced by nonsmoking mothers, infant mortality, including deaths from sudden infant death syndrome (SIDS), is low. The most recent international study of childcare practices in relationship to SIDS rates, conducted by the SIDS Global Task Force, shows dramatically that low SIDS awareness and low SIDS rates are associated with the highest co-sleeping/bed-sharing rates.
At the most recent International SIDS Meeting in Auckland, New Zealand, Sankaran et al. presented data from Saskatchewan, Canada, showing that where breastfeeding and forms of co-sleeping coexist, SIDS deaths are reduced.14 This finding is consistent with a study in South Africa indicating that bed-sharing babies have higher survival rates than solitary-sleeping babies.15
In Hong Kong, where co-sleeping is the norm, SIDS rates are among the lowest in the world.16,17 The same is true in Japan, where rates of not only SIDS but infant mortality in general are among the lowest in the world, according to the Japan SIDS Family Organization’s 1999 report.18 Moreover, during a span of about four years in Japan, where maternal smoking has decreased while breastfeeding, co sleeping, and supine (face up) infant sleep have increased, SIDS rates have decreased—the exact opposite of what co-sleeping critics would predict.
In many other Asian cultures where cosleeping is the norm, including China, Vietnam, Cambodia, and Thailand, SIDS is either unheard of or rare.19,20,21 In one study conducted in Australia, an immigrant Vietnamese mother was told about SIDS, with which she was unfamiliar. She said, “The custom of being with the baby must prevent this disease. If you are sleeping with your baby, you always sleep lightly. You notice if his breathing changes…Babies should not be left alone.” Another Vietnamese mother added, “Babies are too important to be left alone with nobody watching them.”22
Of 40 Chinese women interviewed at Guagzho University Hospital by SIDS researcher Elizabeth Wilson, more than 66% of new mothers intended to have their infants sleep with them in the marital bed, and the rest of her sample planned to have the infant sleep alongside the bed. One informant represented many when she stated that the baby is “too little to sleep alone” and that co-sleeping “makes babies happy.”23
In contrast, in Western urban subgroups, co-sleeping is associated with increased risks to the infant, especially but not exclusively when it occurs in association with maternal smoking, drug or alcohol use, chaotic lifestyles, lack of education and opportunities, prone sleeping, and other dangerous factors.24 For example, bed-sharing deaths (which often erroneously include couch-sleeping deaths in the CPSC data bank) are especially high in the United States among poor African- Americans living in large cities such as Chicago; Cleveland; Washington, D.C.; and St. Louis—the four cities from which data used to argue against the safety of all co-sleeping, regardless of circumstances, emerge.25,26 Moreover, epidemiological studies show consistently across cultures that among economically deprived, indigenous groups, such as the Maori in New Zealand, Aborigines in Australia, Cree in Canada, and Aleuts in Alaska, bed-sharing and other forms of co-sleeping can be associated also with increased risks to infants and increased infant deaths.27,28
The SIDS Global Task Force accounts for these differences in bed-sharing outcomes in a way consistent with my own view, pointing to factors such as parental smoking, drug and alcohol use, infants sleeping prone on soft mattresses, infants sleeping alone on adult beds with gaps or ledges around the bed frame or between the mattress and a wall or piece of furniture, dangerous furniture or furniture arrangements, and infants sleeping next to toddlers or on sofas with obese adults.
Perhaps it is best to conceptualize outcomes related to bed-sharing in terms of a benefit–risk continuum. For example, if mothers elect to bedshare for purposes of nurturing and breastfeeding and are knowledgeable about safety precautions (e.g., use stiff mattresses, do not over-wrap the infant, or lay babies supine), we can expect that bed-sharing will be protective or reduce SIDS risks. But when bed-sharing is not chosen as a childcare strategy but rather is a necessity because there is no other place to put the baby, and mothers smoke, take drugs, and do not place an adult in between a toddler and a baby sharing a bed, increased risk of SIDS or asphyxiation can be predicted.