Co-sleeping

James McKenna founded and ran the Mother-Baby Behavioral Sleep Laboratory at the University of Notre Dame, where he and colleagues spent over three decades documenting the physiology of mother-infant cosleeping. The research used laboratory polysomnography to measure what actually happens during the night when mothers and infants share a bed. The findings have been consistent across studies. Cosleeping mother-infant pairs synchronize sleep stages.

Babies move through more transitions between sleep states, which appears to be protective against the kind of deep sleep that is associated with SIDS in infants who do not yet have full breathing control. Breastfeeding mothers and their infants show even tighter synchrony, and bed-sharing breastfeeding dyads breastfeed twice as often per night as non-bed-sharing pairs, with most of the feeds going unremembered by the mother in the morning. McKenna is the most cited researcher in the cosleeping literature.

Helen Ball runs the Parent-Infant Sleep Lab at Durham University in the UK. Her research focuses specifically on how cosleeping interacts with breastfeeding outcomes.

The headline findings: bed-sharing mothers breastfeed for significantly longer and breastfeed more exclusively than mothers who room-share or sleep separately. In one Durham study, mothers who bed-shared in the first six months were three times more likely to still be breastfeeding at 16 weeks compared with mothers who did not. The mechanism is straightforward.

Babies who feed at night without requiring the mother to fully wake and walk to another room tend to feed more often, which maintains the milk supply and the breastfeeding relationship. The Ball lab data has been instrumental in shifting UK public health guidance toward acknowledging safe bed-sharing as a real category.

The Safe Sleep 7 is a set of conditions developed by researchers including McKenna, La Leche League International, and analyzed against datasets including the work of Peter Blair. The conditions describe when bed-sharing has been associated with the same or lower risk profile as separate sleeping.

The seven conditions: the mother does not smoke, is sober (no alcohol or sedating drugs), is breastfeeding, has a healthy full-term baby, places the baby on its back, the baby is lightly dressed and unswaddled, and the bed is firm with no pillows, gaps, or soft bedding near the baby's face. When all seven conditions are met, the SIDS risk associated with bed-sharing drops substantially in the available data. The Bombard et al.

CDC paper in 2018 documented the trends in safe sleep practices. The framework gives a structured way for parents to assess whether their specific bed-sharing context is the kind that the research supports.

Peter Blair and colleagues used data from the Avon longitudinal study, one of the largest UK birth cohorts, to examine SIDS risk in bed-sharing infants under different conditions. The headline finding: in non-smoking parents who had not consumed alcohol or sedating drugs, bed-sharing with a healthy full-term breastfed infant on a regular bed showed no increased SIDS risk compared with separate sleeping.

The risk emerged specifically when smoking, alcohol, soft bedding, or sofa-sleeping entered the picture. The paper appeared in BMJ Open in 2014. The work has been important in shifting the public health conversation from "bed-sharing is dangerous" to "bed-sharing under specific conditions is the problem." Blair's group has continued to publish updates that consistently support the conditional safety framing.

Melissa Bartick is a US researcher who has published extensively on infant feeding and sleep safety. Her work, including a 2019 paper with Cecília Tomori, drew a sharp distinction that the AAP has often blurred. Sofa-sleeping with an infant is among the highest-risk infant sleep arrangements identified in the data, while bed-sharing under safe conditions is much lower risk.

Bartick's argument has been that conflating the two in public health messaging actively drives unsafe outcomes, because mothers who fall asleep nursing on a couch (often because they have been told never to bring the baby into the bed) end up in the most dangerous configuration. The paper called for the AAP to revise its messaging to distinguish bed-sharing from sofa-sleeping. As of 2026, the AAP has not done so.

The UNICEF UK Baby Friendly Initiative is the British arm of the global UNICEF/WHO Baby Friendly program, which sets standards for maternity and infant feeding services. Its position on bed-sharing differs sharply from the AAP.

UNICEF UK explicitly recognizes that bed-sharing happens in most breastfeeding families regardless of public health messaging, and provides safe bed-sharing guidance rather than blanket discouragement. The guidance is based on the conditional-safety evidence from Blair and others.

The UK NHS adopted aligned messaging in 2014, and Lullaby Trust, the UK's main SIDS charity, has supported safe bed-sharing guidance since then. The contrast with US public health messaging is direct. Both countries read the same research base.

The 2015 McKenna and Gettler paper in Acta Paediatrica argued for a conceptual reframing. The title states their position: "There is no such thing as infant sleep, there is no such thing as breastfeeding, there is only breastsleeping." The argument is that mother-infant cosleeping with breastfeeding is so physiologically integrated that treating them as separate behaviors misrepresents the biology.

Babies who sleep near their mother feed more often, regulate their breathing and temperature in response to the mother's, and show measurable differences in physiological state compared with infants who sleep separately. The paper has been cited widely in the evolutionary anthropology and lactation literature, and is one of the most influential recent papers on the conceptual basis of cosleeping research.

The Mileva-Seitz, Bakermans-Kranenburg, Battaini and Luijk review in Sleep Medicine Reviews systematically examined 659 published papers on parent-child bed-sharing. The review pulled together evidence on socioeconomic and cultural correlates of the practice, purported risks (including SIDS and sleep problems), and developmental outcomes including attachment, cognitive development, behavioral outcomes, and parent-child relationship measures.

The pooled finding on outcomes was that bed-sharing had either no association or a positive association with the developmental measures studied, and no consistent evidence of negative effects on attachment, independence, or social development. The review covered cosleeping practices across cultures. The conclusion noted that the cultural narrative warning that cosleeping creates dependent or maladjusted children is not supported by the developmental research base.

Melvin Konner (Emory) and Meredith Small (Cornell) are two anthropologists whose work documented infant sleep practices across cultures. Konner's work with the Ju/'hoansi people of the Kalahari documented continuous mother-infant contact day and night, with no separate infant sleep arrangements.

Small's book 'Our Babies, Ourselves' synthesized cross-cultural data from dozens of societies, including the rapidly shrinking number that still practiced traditional infant care. The pattern was consistent.

Separating mothers and infants for sleep is a recent practice, largely confined to industrialized Western societies, and it represents a sharp departure from what infants have evolved to expect. This does not by itself prove cosleeping is better. It does establish that the species norm is cosleeping, and that the burden of proof should sit on the practice that is the historical anomaly.

The American Academy of Pediatrics issued updated Safe Sleep Recommendations in 2022, maintaining its long-standing position that bed-sharing should be avoided for all infants under one year of age. The AAP cites pooled SIDS data showing elevated risk for bed-sharing infants, particularly in the first three months.

The recommendation does not differentiate between safe and unsafe bed-sharing contexts. The AAP position is the strongest opposing evidence to the cosleeping case, and it carries weight because the AAP is the dominant US pediatric authority.

The criticisms of the AAP position, including those from Bartick and McKenna, are that the data pools together fundamentally different situations (sofa-sleeping, smoking, alcohol, soft bedding, breastfed vs formula-fed) and assigns the risk to bed-sharing as a category rather than to the specific risk factors. The AAP has been asked to revise its messaging multiple times. It has not done so.

Wennergren and colleagues published a 2021 paper in Acta Paediatrica analysing Swedish national surveys of infant sleep practices over 15 years. Bed-sharing among 6-month-old infants nearly doubled, rising from 20 percent in the 2003-2004 survey to 33 percent in 2018.

The surveys also found a strong positive correlation between bed-sharing and breastfeeding rates. Sweden has one of the lowest infant mortality rates in the world (2.1 per 1,000 live births, compared with the US 5.1), and bed-sharing has been rising over the same period that infant mortality has been falling. The Swedish National Board of Health and Welfare (Socialstyrelsen) introduced a bed-sharing warning in 2013 aimed at preventing SIDS, but the gap between official guidance and family practice is wide and known to the agency, which has been reviewing its recommendations after criticism from parents and specialists.