“100 years of rapidly changing infant-care fashions cannot alter several million years of evolutionarily derived infant physiology”

̴ Dr. Helen Ball

Sleep and feeding have become some of the most discussed and disseminated topics in parenting today.  How much sleep are you getting?  Do you use formula or just the breast?  When should a child sleep through the night?  Do you pump?  Does dad feed the little one at all?  Do you room-share, bedshare, or put the little one alone in his room?  What about sex?   There is an endless array of questions and judgments and ‘should’s associated with both infant sleep and feeding.  But this hasn’t always been the case.  It used to be a simple matter of mother breastfeeding and mother and infant sleeping together with no judgment and no questions about quality or quantity of sleep.  For this reason, breastfeeding and co-sleeping are huge parts of evolutionary parenting; they facilitate the bond between mother and infant via skin-to-skin contact

[1], co-sleeping works to keep baby’s temperature and breathing regulated[2][3] and it seems to provide parents and baby with better sleep[4], while breastfeeding offers vital immune protection to infants necessary for survival[5].

For most mothers in contemporary Western societies, breastfeeding and infant sleeping arrangements are two distinct parenting practices with little or no relation to one another.  To talk about one is not to talk about the other.  Biologically, however, the two are inextricably intertwined.  For much of human history, hunter-gatherer societies dominated and in this domain, women were as central to the survival of the clan as men.  There were no maternity leaves, but the work done by women was of the less-dangerous gatherer type, meaning they were able to do their work with children and infants in tow.  But with this came the necessity for women to sleep well as a woman who is sleep-deprived does not serve anyone well in any capacity (it is truly strange that we have adopted the modern view that sleep deprivation is a “normal” state of affairs with a newborn).  As for the infant, without any alternatives, they required their mother’s breastmilk to survive, much less thrive.  And thus we reach the point at which breastfeeding and co-sleeping collide – in order to breastfeed continuously without immense sleep interruption mothers must co-sleep; and on the flipside, co-sleeping allows mothers to breastfeed more often providing more nutrition for a developing infant.  Biologically, our bodies have evolved to both breastfeed and co-sleep and each seems to have helped facilitate the other.  So how did this separation occur and what does it mean for infant well-being and parenting practices in Western societies?

There seem to be distinct reasons for the reduction in breastfeeding and co-sleeping in Western societies, yet they obviously affect each other.  With respect to breastfeeding, we see the rise of the industrial society, which sent women to work, and science with all its might creating formula which was believed to be superior to breastmilk by doctors for quite some time (for a full summary of this, see Why Is Saving Babies’ Lives Not Enough?).  These two factors alone had a huge impact on reducing breastfeeding rates in Western societies.  This reduction of breastfeeding meant that sleeping arrangements were also free to change, but in addition there was an even greater impetus for change – the belief in fostering independence.

The juxtaposition of a baby’s dependence/interconnectedness and independence/autonomy has dictated parenting practices around the world, though not always in the same manner.  For example, in America the newborn is viewed as entirely dependent upon its mother, yet the desired end-goal is for that baby to be an independent and autonomous individual.  Thus our practices are geared towards that end-goal; we put babies alone in their own room, we don’t touch them very often, and we’ve even removed the dependence on mom for breastfeeding through the use of formula.  In contrast, the Japanese view the newborn as an autonomous, independence being who must be held, breastfed, and touched regularly (co-sleeping is the norm there) in order to build the feelings of interconnectedness they value[6].  Similarly, research from New Zealand has found that cultural groups that share the Western independence view rarely sleep with their infants, while Pacific cultural groups demonstrate lots of sleep contact because they believe that interconnectedness is the way to foster a child’s development[7].  So while there are myriad factors why any one individual would choose to co-sleep or not, or breastfeed or not, culturally this notion of independence has played a very large role in shaping our collective views on the issue.

The problem for Western cultures is that the Western assumptions of what fosters independence seem to be, well, wrong.  Research has demonstrated that the Eastern interconnectedness model fosters independence and well-being to a much greater degree than simply forcing children to try and be independent.  One such example is the case of the Sami and Norwegian children.  Sami individuals are more likely to co-sleep with their children and their children were found to be more independent and demand less attention from their parents than Norwegian children who typically sleep alone[8].  (For a full summary of the link between independence and co-sleeping, see Co-Sleeping: Fostering Independence.)  Interestingly, thanks to a push to increase breastfeeding rates in Norway, co-sleeping has also become a more common sleeping arrangement[9] and children are reaping the benefits.  Similar relationships have also been found in Sweden where breastfed infants were much more likely to sleep with their parents than formula-fed infants[10].

I have mentioned some of the logistical reasons for breastfeeding and co-sleeping to go together, but is there more than that?  After all, if it’s a matter of pure logistics, wouldn’t it simply be a matter of whatever works to separate the two?  Turns out there are a couple rather important effects that each practice has on the other and we’ll start with the effects of co-sleeping on breastfeeding.  As previously mentioned, co-sleeping is greater amongst breastfeeding mothers[11], and while increasing breastfeeding has increased co-sleeping rates[9][10], the fact it that co-sleeping actually facilitates more breastfeeding.  If you compare mothers who breastfeed, those who co-sleep breastfeed up to twice as much at night over those who do not co-sleep[12].

Why is this important?  Dr. Helen Ball has done research on the effects of sleep location on breastfeeding and come to some rather interesting (though expected) conclusions.  Namely, co-sleeping right from the start reduces the chances of having breastfeeding problems.  Specifically, Dr. Ball looked at sleep locations for new mothers and their infants and randomly assigned women to one of three location types – either those that facilitated mother-infant access (i.e., bed-sharing or putting the infant in a three-sided crib that was attached the parent bed, much like an official Co-Sleeper) or those that did not (i.e., a standalone bassinette next to the mother’s bed).  Mother-infant dyads who had sleeping arrangements that facilitated mother-infant access showed greater successful suckling than those who were in the standalone bassinette group[13].  Upon follow-up with these same mothers, it was found that these effects of early co-sleeping continued at 16 weeks, with twice as many mothers in the unhindered access groups both breastfeeding and exclusively breastfeeding[14].  Note that this doesn’t even cover women who may have their newborns in a separate room from themselves as all three groups were at the very least room-sharing, but it was the bed-sharing (or three-sided crib) that facilitated breastfeeding.  Why does this happen?  As previously mentioned, infants who co-sleep tend to feed (or at least suckle) for twice the amount of time as non-co-sleeping infants[11].  Stimulation of the nipple is necessary for the production of prolactin, the hormone that allows for milk secretion, and thus the reduction in suckling or nursing can lead to deleterious effects on milk production or the maintenance of a mother’s milk supply[15].  In short, by getting your baby into bed with you right away, you reduce the chances of having supply issues when breastfeeding.

Now, what of the effects of breastfeeding on co-sleeping?  First you must remember that the biggest argument against co-sleeping is to do with infant deaths.  Many people argue that co-sleeping increases the risk of death via suffocation or SIDS.  While there is no direct evidence that breastfeeding causes a reduction in SIDS for co-sleeping babies, there is ample circumstantial evidence to suggest this is the case.  Most prominently, cross-cultural data shows that cultures in which co-sleeping and breastfeeding are the norm have substantially lower SIDS rates than cultures in which they are not the norm[16][17][18].  For example, Japan has long been considered the pinnacle of success with respect to SIDS deaths as their rates are generally half of other industrialized nations and co-sleeping is also the norm there (see Bedsharing and SIDS: The Whole Truth for a full review of their practices and SIDS rates).  It is possible that breastfeeding has nothing to do with their lower SIDS rates, except that we know breastfed babies are at a much lower risk for SIDS more generally[19][20][21][22][23].  Breastfeeding in and of itself reduces the risk of SIDS; in a meta-analysis on the relationship between breastfeeding and SIDS, it was found that while any breastfeeding more than halves the risk of SIDS, exclusive breastfeeding has an ever greater effect[24].  Furthermore, duration and intensity of breastfeeding have also been found to relate to SIDS levels, with greater duration and intensity leading to a lower risk of SIDS[3].  If you recall, it has also been found that co-sleeping babies breastfeed up to twice as long as non-co-sleeping babies.  It is therefore reasonable to assume that the extra breastfeeding during co-sleeping serves as added protection against SIDS.

An additional hypothesis for how breastfeeding may reduce the risk of SIDS for co-sleeping infants comes from Dr. James McKenna who has posited that the arousals from breastfeeding keep the infant from falling into a deeper sleep which may lead to a “failure to rouse” [25].  This “failure to rouse” has been discussed as a potential mechanism behind SIDS – infants reach too deep a level of sleep and they are simply incapable of coming out of it, kind of like entering a coma.  Breastfeeding thus increases the number of infant arousals (though not full wakings) and this is greater during co-sleeping and is especially true for breastfeeding dyads not only because of mom’s movements, but because of the frequency of feedings.

Another way in which breastfeeding may help reduce the risk of SIDS (and did for many years) is by the position in which the infant sleeps.  Breastfeeding infants are less likely to sleep prone because it doesn’t facilitate breastfeeding as easily; in order for an infant to breastfeed, he or she needs to be on his or her back or side.  An infant in the prone position simply cannot reach or latch onto the breast (unless the prone position is on mom).  This also helps reduce the chances of infants suffocating, as a baby in the prone position who cannot roll over is at greater risk for suffocation.

Indeed, breastfeeding also seems to be related to practices that reduce the risk for suffocation.  Research has found that maternal-infant behaviour in bed is different amongst breastfeeding mothers than formula-fed infants[26] with certain behaviours, like facing the infant and having the infant lie at chest level, being much more prominent in breastfeeding dyads.  Dr. Helen Ball has done this work and while some of these behaviours may seem trivial, they can be imperative for keeping an infant safe.  For example, a child who lies at chest level (as opposed to head level, which is what Dr. Ball found to be more common in formula-fed infants who co-slept) is less likely to be surrounded by pillows which are considered dangers for suffocation.  They are also less likely to be too close to a headboard which is a known hazard as babies have fallen between the headboard and mattress and suffocated.

I would also like to add my own hypothesis here.  There is evidence that bonding is generally greater for breastfeeding dyads – the reason being that there seems to be more eye contact between mom and baby during a breastfeeding session than a bottle-feeding session[27].  I believe that the bonding that occurs during daytime feedings serve to heighten mom’s awareness of and about her baby, leading her to be intuitively safer at night.  That is, a mother who has bonded with her child is more aware of her child’s presence at any given point and I believe this extends to when we are sleeping (barring the use of any illicit substances).  Of course, research needs to be done to test this – it’s just educated speculation at this point, but I struggle with the idea that all this bonding doesn’t extend its effects into the evening hours.

Hopefully the link between breastfeeding and co-sleeping is now clear.  The benefits they offer each other are neither superfluous nor easily available by other means.  In changing our parenting practices, we have developed other problems.  Western countries have alarmingly high rates of breastfeeding problems and much higher rates of infant mortality (notably SIDS) than other countries who have similar medical advancements but also breastfeed and co-sleep on a regular basis.  Interestingly, we also have a high rate of sleeplessness by new mothers – so much so that we joke about never sleeping again when people have a new baby – and our children have unusually strong attachments to objects for sleep (e.g., security blankets, stuffed animals).  Neither of these are universal.  In fact, research has shown that breastfeeding mothers who co-sleep get more sleep than both bottle-feeding mothers and mothers who breastfeed, but do not co-sleep[28].  Additionally, children who are solitary sleepers show a greater need and use for security objects and sleep aids[29].  So not only do our sleep and feeding practices have significant consequences (i.e., breastfeeding troubles and infant death), we see smaller consequences in the majority of new moms and their children.  Isn’t it time we recognized not only the benefits of co-sleeping and breastfeeding, but the symbiotic nature of the two?

Did you co-sleep?  Breastfeed?  Did you experience any of the deficits/benefits associated with your particular feeding and sleeping style?



[2] Ball HL. “New” practice of bedsharing and risk of SIDS. The Lancet (2004); 363: 1558.

[3] McKenna JJ & McDade T. Why babies should never sleep alone: A review of the co-sleeping controversy in relation to SIDS, bedsharing and breast feeding. Paediatric Respiratory Reviews (2005); 6: 134-152.

[4] McKenna JJ, Ball HL, & Gettler LT. Mother-infant co-sleeping, breastfeeding and sudden infant death syndrome: What biological anthropology has discovered about normal infant sleep and pediatric sleep medicine. Yearbook of Physical Anthropology (2007); 50: 133-161.

[5] Duijts L, Jaddoe VWV, Hofman A, & Moll HA.  Prolonged and exclusive breastfeeding reduces the risk of infectious diseases in infancy.  Pediatrics 2010; 126: e18-e25.

[6] Caudill W & Weinstein H. Maternal care and infant behaviour in Japan and America. Psychiatry (1969); 32:12–43.

[7] Abel S, Park J, et al. Infant care practices in New Zealand: a cross-cultural qualitative study. Social Science Medicine (2001); 53:1135–1148.

[8] Arnestad M, Andersen M, Vege A & Rognum TO. Changes in the epidemiological pattern of sudden infant death syndrome in southeast Norway, 1984–1998: implications for future prevention and research. Arch Dis Child (2001); 85:180–185.


[10] Lindgren C, Thompson JMD, Haggblom L & Milerad J. Sleeping position, breastfeeding, bedsharing and passive smoking in 3-month-old Swedish infants. Acta Paediatr (1998); 87: 1028–1032.

[11] Blair PS & Ball HL. The prevalence and characteristics associated with parent-infant bed-sharing in England. Arch Dis Child (2004); 89: 1106-1110.

[12] McKenna JJ, Mosko S & Richard C. Bedsharing promotes breast feeding. Pediatrics (1997); 100:214–219.

[13] Ball HL. Bed-sharing on the post-natal ward: breastfeeding and infant sleep safety. J Can Paediatric Soc (2006); 11:43A–46A.

[14] Ball HL, Klingaman KP. Breastfeeding and mother-infant sleep proximity: implications for infant care. In: Trevathan W, Smith EO, McKenna JJ. Evolutionary medicine, 2nd ed (2007). New York: Oxford University Press. p 226–241.

[15] Neville MC, Morton J & Umemura S. Lactogenesis: the transition from pregnancy to lactation. Pediatr Clin North Am (2001); 48:35.

[16] Nelson EAS & Taylor BJ. International child care practices study: infant sleeping environment. Early Human Development (2001); 62:43–55.

[17] Watanabe N, Yotsukura M, Kadoi N, Yashiro K, Sakanoue M & Nishida H. Epidemiology of sudden infant death syndrome in Japan. Acta Paediatr Jpn (1994); 36:329–332.

[18] Lee NY, Chan YF, Davies DP, Lau E & Yip DCP. Sudden infant death syndrome in Hong Kong: confirmation of low incidence. British Medical Journal (1989); 298:721.

[19] Ip S, Chung M, & Raman G. Breastfeeding and maternal and infant health outcomes in developed countries, evidence report/technology assessment number 153. Agency for Healthcare Research and Quality, Rockville, MD (2007). http://www.ahrq.gov/clinic/tp/brfouttp.htm (Accessed July 16, 2011)

[20] Hoffman H, Damus K, Hillman L & Krongrad E. Risk factors for SIDS: results of the institutes of child health and human development SIDS cooperative epidemiological study. In: Schwartz P, Southall D, Valdes-Dapena M, editors. Sudden infant death syndrome: cardiac and respiratory mechanisms. Ann NY Acad Sci (1988); 533:13–30.

[21] Mitchell EA, Taylor BJ, Ford RPK, Stewart AW, Becroft DM, Thompson JW, Scragg R, Hassall IB, Barry DM & Allen EM. Four modifiable and other major risk factors for cot death: the New Zealand study. J Paediatr Child Health (1992); Suppl 1:S3–S8.

[22] Ford RP, Taylor BJ, Mitchell EA, Enright HW, Stewart AW, Becroft DM & Scragg R. Breastfeeding and the risk of sudden infant death syndrome. Int J Epidemiol (1993); 22:885–890.

[23] Fredrickson DD, Sorenson JF & Biddle AK. Relationship of sudden infant death syndrome to breast-feeding duration and intensity. Am J Dis Child (1993);147:460.

[24] Hauck FR, Thompson JMD, Tanabe KO, Moon RY, & Vennemann MM. Breastfeeding and risk of sudden infant death syndrome: A meta-analysis. Pediatrics (2011); 128: 1-10.

[25] Mosko S, Richard C, & McKenna JJ. Infant arousals during mother-infant bed sharing: Implications for infant sleep and sudden infant death syndrome research. Pediatrics (1997); 100: 841-849.

[26] Ball HL. Parent-infant bed-sharing behavior: effects of feeding type, and presence of father. Human Nature (2006); 17:301–316.

[27] Else-Quest NM, Hyde JS, Clark R. Breastfeeding, bonding, and the mother-infant relationship. Merrill-Palmer Quarterly, 49, 495-517.

[28] Quillin SIM & Glenn LL. Interaction between feeding method and co-sleeping on maternal-newborn sleep. Journal of Gynecology and Neonatal Nursing (2003); 33: 580-588.

[29] Hayes MJ, Roberts SM, & Stowe R. Early childhood co-sleeping: Parent-child and parent-infant nighttime interactions. Infant Mental Health Journal (1996); 17: 348-357.


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