What causes Sudden Infant Death Syndrome (SIDS)?

What Causes Sudden Infant Death Syndrome (SIDS)

SIDS is caused by a convergence of multiple factors according to the "Triple-Risk Model," which includes intrinsic vulnerability (especially brainstem abnormalities affecting arousal and cardiorespiratory control), a critical developmental period (typically 1-4 months of age), and external stressors (such as prone sleeping position, soft bedding, or tobacco exposure). 1

The Triple-Risk Model of SIDS

The most widely accepted explanation for SIDS is the Triple-Risk Model, which requires the simultaneous presence of:

1. Intrinsic Vulnerability:

   • Brainstem abnormalities in the medullary serotonergic (5-HT) system are found in up to 70% of SIDS cases 1
   • These abnormalities affect areas responsible for coordinating respiratory, arousal, and autonomic functions 1
   • Genetic variations may increase vulnerability, including cardiac sodium or potassium channel mutations (in 5-10% of SIDS cases) 1

2. Critical Developmental Period:

   • 90% of SIDS cases occur before 6 months of age 1
   • Peak incidence occurs between 1-4 months of age 1
   • This period coincides with rapid development of circadian rhythms, autonomic control, and arousal mechanisms 2

3. External Stressors:

   • Prone or side sleeping position 1
   • Soft bedding or unsafe sleep surfaces 1
   • Overheating or overbundling 1
   • Exposure to tobacco smoke 1
   • Bed-sharing, particularly with parents who smoke or use substances 1

Pathophysiological Mechanisms

The convergence of these risk factors ultimately results in:

• Progressive asphyxia 1
• Bradycardia 1
• Hypotension 1
• Metabolic acidosis 1
• Ineffectual gasping, leading to death 1

Specific Neurological Abnormalities

Research has identified specific neurological issues in SIDS victims:

• Abnormalities in the brainstem's serotonergic (5-HT) system affect arousal responses to dangerous situations during sleep 1
• Decreased 5-HT 1A receptor binding and relative decrease in binding to the serotonin transporter 1
• These abnormalities may prevent normal protective responses to stressors that commonly occur during sleep 1

Environmental and Maternal Risk Factors

Several environmental and maternal factors increase SIDS risk:

• Prenatal tobacco exposure: Alters nicotinic acetylcholine receptor expression in brainstem areas important for autonomic function 1
• Maternal alcohol use: Associated with 6-8 times increased SIDS risk 1
• Illicit drug exposure: Prenatal exposure to opiates, cocaine, and cannabis associated with increased risk 1
• Low birth weight or growth restriction: Suggests adverse intrauterine environment 1

Demographic and Epidemiological Patterns

Important demographic patterns include:

• Higher risk in male infants 1
• Racial disparities exist, with higher rates among Black and Indigenous populations 1
• Historically, SIDS was more common in colder months, but this seasonal pattern has diminished over time 1

Prevention Through Modifiable Risk Factors

The dramatic decline in SIDS rates since the 1990s demonstrates that addressing modifiable risk factors can significantly reduce mortality:

• Sleep position: Supine (back) sleeping reduces risk significantly compared to prone or side positions 1
• Sleep environment: Firm sleep surface without soft objects or loose bedding 1
• Room-sharing without bed-sharing: Reduces risk while facilitating breastfeeding 1
• Avoiding smoke exposure: Both prenatal and environmental tobacco smoke increase risk 1
• Avoiding alcohol and illicit drugs: Particularly important during pregnancy and when caring for infants 1

Important Clinical Considerations

• Despite common misconceptions, supine sleeping does not increase choking risk 1
• Home cardiorespiratory monitors are not recommended for SIDS prevention 1
• Breastfeeding is protective against SIDS 1
• Pacifier use at sleep time is associated with reduced SIDS risk 1
• Regular immunizations according to schedule reduce SIDS risk 1

Understanding the multifactorial nature of SIDS helps explain why no single intervention completely eliminates risk, but addressing modifiable factors has proven highly effective in reducing SIDS mortality.