Lead
Co-sleeping has a long history as a cultural practice in Japan. Sleeping together — parent and infant in the same futon — has been discussed in terms of ease of night nursing and parent-infant closeness.
English-language guidelines, by contrast, take the position that bed-sharing raises SIDS risk and recommend room-sharing without bed-sharing (infant in a separate sleep surface, in the same room as the parent).
What is the evidence behind these two positions, where do they agree, and where do they differ? This article maps the research.
The AAP's Position — 2022 Updated Guidelines
The American Academy of Pediatrics updated its guidelines on safe infant sleep environments in 2022 [1]. The core recommendations:
- Room-sharing without bed-sharing is recommended for at least the first six months (ideally 12 months)
- Bed-sharing on sofas, armchairs, or cushioned chairs is strongly contraindicated (this configuration is associated with particularly high SIDS risk)
- Supine sleep position should be maintained consistently
The primary study behind the AAP's explicit characterization of bed-sharing as a risk factor is a 2013 case-control study: research design comparing people who have an outcome with those who don't, looking backward for risk factors by Carpenter et al. [2]. Drawing on pooled data from five countries in the ECAS study, the reported odds ratios for bed-sharing were:
- Infants under 3 months, no hazard factors (non-smoking, non-drinking parents): OR = 2.89
- Infants under 3 months, parents had been drinking: OR substantially higher
The 2022 revision also added somewhat more nuanced language, noting the importance of environmental design to reduce the likelihood of accidentally falling asleep on a sofa — acknowledging that bed-sharing sometimes happens unintentionally.
Reading the Numbers — Relative Risk Versus Absolute Risk
Understanding Carpenter et al.'s OR of 2.89 requires a comparison with absolute risk.
In Japan, the SIDS incidence is approximately 0.09 per 1,000 live births (2020 vital statistics) — one of the lowest rates in the world. In Western countries, baseline rates are roughly 0.3–0.6 per 1,000 live births.
An OR of 2.89 means the risk is 2.89 times higher. But if the baseline rate is 0.3 per 1,000, a 2.89-fold increase yields an absolute risk: the actual probability of an outcome occurring, expressed as a rate rather than a ratio to another group of approximately 0.87 per 1,000. This is not an argument that the risk is trivial; it is an argument that using relative risk alone, without reference to the underlying baseline, can make risk factors appear larger than their actual population-level contribution. Distinguishing relative from absolute risk is essential for communicating the magnitude of any risk accurately [3].
James McKenna's Research — Behavioral Observation and Anthropology
Medical anthropologist and sleep researcher James McKenna has proposed the concept of breastsleeping and has offered a sustained counterpoint to the AAP position [4].
McKenna et al.'s polysomnography: a multi-channel sleep study measuring brain waves, oxygen, heart rate, and breathing to analyze sleep architecture studies found that mothers who co-sleep show higher frequencies of arousal during feeding and in response to infant breathing changes; infants' sleep architecture (arousal and transition patterns) is also affected [4]. From this perspective, co-sleeping is not a simple risk factor but a physiologically complex mutual regulatory system between parent and infant.
There is also an epidemiological observation that complicates a simple reading: SIDS rates in countries where co-sleeping is culturally normative — Japan, Korea, Southeast Asia — tend to be lower than in Western countries [5]. This does not constitute direct evidence that co-sleeping is protective. The comparison involves substantial confounders: differences in living environments, healthcare infrastructure, and diagnostic criteria. But it does raise questions about whether bed-sharing per se is the relevant variable.
Where the Research Agrees — Conditions That Elevate Risk
Despite their differences in framing, the AAP guidelines and McKenna's research agree on the conditions that substantially increase the risk associated with bed-sharing [1,2]:
- Alcohol, drugs, or sedating medications (the largest contributor)
- Parental smoking
- Falling asleep on a sofa, armchair, or cushioned chair (the condition the AAP most strongly opposes)
- Soft bedding, excess pillows, loose or bunched sheets
- Infants younger than 3 months (highest-risk period)
When these conditions are stacked, the odds ratios increase dramatically. Conversely, when none of these conditions are present, the risk profile is substantially lower than when they are.
Practical Takeaways
1. Check for risk-elevating conditions Alcohol, smoking, sedating medications, and sofa sleep are risk factors that research consistently identifies as dangerous. Bed-sharing under any of these conditions is worth avoiding — independent of where one stands on the broader guidelines.
2. Room-sharing as a middle option Room-sharing without bed-sharing — recommended by the AAP — preserves easy awareness of night waking (the parent is close enough to hear and respond) while reducing the risk factors associated with bed-sharing [1]. For many families it is a workable compromise.
3. Prioritize a firm sleep surface Whether or not bed-sharing is chosen, removing soft bedding, excess pillows, and loose sheets is the single most consistently supported safety measure across multiple studies [1,2].
Summary
The AAP guidelines and McKenna's research reach different conclusions about whether all bed-sharing is dangerous, but they converge on the conditions — alcohol, smoking, sofas, soft bedding — that substantially raise risk. Holding the relative/absolute risk distinction in mind, and checking those conditions against one's own household situation, is the most useful way to engage with this literature.
If the decision is unclear, a pediatrician is the appropriate person to consult.
References
- Moon RY, Carlin RF, Hand I; AAP Task Force on Sudden Infant Death Syndrome and the AAP Committee on Fetus and Newborn. Sleep-related infant deaths: updated 2022 recommendations for reducing infant deaths in the sleep environment. Pediatrics. 2022;150(1):e2022057990. doi:10.1542/peds.2022-057990. PMID: 35782619.
- Carpenter R, McGarvey C, Mitchell EA, et al. Bed sharing when parents do not smoke: is there a risk of SIDS? An individual level analysis of five major case-control studies. BMJ Open. 2013;3(5):e002299. doi:10.1136/bmjopen-2012-002299. PMID: 23793691.
- Gigerenzer G, Gaissmaier W, Kurz-Milcke E, Schwartz LM, Woloshin S. Helping doctors and patients make sense of health statistics. Psychol Sci Public Interest. 2007;8(2):53–96. doi:10.1111/j.1539-6053.2008.00033.x. PMID: 26158984.
- McKenna JJ, Gettler LT. There is no such thing as infant sleep, there is no such thing as breastfeeding, there is only breastsleeping. Acta Paediatr. 2016;105(1):17–21. doi:10.1111/apa.13161. PMID: 26762677.
- Mindell JA, Sadeh A, Wiegand B, How TH, Goh DY. Cross-cultural differences in infant and toddler sleep. Sleep Med. 2010;11(3):274–280. doi:10.1016/j.sleep.2009.04.012. PMID: 20138578.