Resilience: What protects infants from SIDS?

Sudden Infant Death Syndrome (SIDS) has so far been described mainly from a risk perspective. According to this perspective, internal biological, external environmental and temporal risk factors interact to facilitate this catastrophic event.

While these factors clearly play a role, their overall explanatory power appears to be low: the vast majority of infants do not die of SIDS despite exposure to one or more risk factors.

The authors discuss the limitations of the classic risk-based explanatory model using the two most frequently discussed risk factors for SIDS, prone positioning and bed-sharing. Based on these examples, they bring together findings from evolutionary theory, comparative behavioral research and developmental pediatrics to develop a new explanatory model.

According to this “evolutionary-developmental model,” SIDS may be better understood if the question of resilience is also addressed: Which protective factors may be missing in infants who die from SIDS, and how do those factors normally develop?

With this question in mind, the authors describe SIDS as an imbalance between the biological-regulatory challenges an infant currently faces and the infant’s currently available abilities for self-protection.

Concretely, the theory proposes that this imbalance may lead to SIDS when an infant has not developed adequate protective behavioral skills and is then subjected to a situation that requires a high degree of physiological regulation—for example, after slipping into the prone position.

Within the model, SIDS appears centrally as an expression of insufficient developmental resources and therefore as a developmental condition. The authors draw on evolutionary theory, which assumes that the development of a human infant in a species-typical environment should allow sufficient protective resources to develop. They therefore consider SIDS a possible example of evolutionary maladaptation: a constellation in which certain modern developmental influences may undermine part of the infant’s evolved repertoire.

In summary

The authors argue that SIDS may be better understood if the focus on risk factors is complemented by a deeper understanding of the protective factors human infants acquire during normal development.

They analyze and test this theory against epidemiological and experimental findings from SIDS research and neurodevelopmental research. They also address the unresolved question of why breastfeeding is associated with a lower risk of SIDS.

The model may offer new questions for research and public-health practice. A major difficulty is that risk factors for SIDS occur in the vast majority of families, yet only in a tiny number of cases do they translate into the tragic outcome of SIDS. A better understanding of protective factors may help researchers define groups of vulnerable infants more precisely and investigate ways of supporting protective development.

This is a theoretical model, not a clinical trial or a new set of sleep recommendations. Established safe-sleep guidance continues to apply.

Publication

Renz-Polster H, Blair PS, Ball HL, Jenni OG, De Bock F. “Death from Failed Protection? An Evolutionary-Developmental Theory of Sudden Infant Death Syndrome.” Human Nature. 2024;35:153–196. Read the full paper at PubMed Central.

For the argument’s scientific background, read Don’t Forget the Guardian Angels. For the developmental mechanism in detail, continue with What protects infants from SIDS?