Infants who resided at an altitude of 8,000 ft or higher were at 2.3 times greater risk of SIDS, compared with infants who lived at an altitude below 6,000 ft.
Sudden infant death syndrome (SIDS) is the cause of around 3,500 infant deaths in the US every year, making it the third leading cause of infant deaths in the country and the leading cause of death among infants aged under 1 year.
While many cases of SIDS cannot be explained, most occur as a result of an unsafe sleeping environment. In July 2014, for example, Medical News Today reported on a study citing bed-sharing with infants as the greatest risk factor for SIDS.
The researchers of this latest study - including Dr. David Katz of the Division of Cardiology at the University of Colorado School of Medicine - say that hypoxia is a common theory in cases of SIDS, whereby an infant is deprived of oxygen.
Hypoxia may occur at high altitudes, where oxygen levels are lower. "Infants living at altitude have evidence of hypoxia," note the authors. "However, the association between SIDS incidence and infant residential altitude has not been well studied."
Infants living at 8,000 ft or higher at 2.3 times increased risk of SIDS
To further assess the link between SIDS and high altitude, Dr. Katz and colleagues analyzed 2007-12 data from Colorado birth and death registries, identifying 393,216 infants born during this period.
The team determined the residential altitude of infants by geocoding the residential address of parents. Around 79.6% of infants lived at an altitude below 6,000 ft, 18.5% lived at an altitude of 6,000-8,000 ft, while 1.9% resided at an altitude of 8,000 ft or above.
In addition, the researchers analyzed SIDS rates at various altitudes in Colorado between 1990 and 2012 in order to assess the impact of the Back to Sleep Campaign (now the Safe to Sleep Campaign) - launched in 1994 to promote sleep safety for infants - on SIDS incidence.
The results of the study revealed that infants who resided at an altitude of 8,000 ft or higher were at 2.3 times greater risk of SIDS, compared with infants who lived at an altitude below 6,000 ft.
This association was independent of other risk factors for SIDS, including parental age, race, education and socioeconomic status, infants' age and breastfeeding status and maternal smoking status.
The researchers also confirmed a separate link between low birth weight, tobacco exposure and low socioeconomic status and increased risk of SIDS.
Following safe sleep guidelines may reduce altitude-associated SIDS risk
The Back to Sleep Campaign was found to similarly reduce SIDS incidence in Colorado across all altitudes. Overall, the team found a drop in SIDS incidence from 1.99 per 1,000 live births before the campaign to 0.57 per 1,000 live births after its launch.
This finding, the researchers say, indicates that parents with young infants who live at high altitudes can reduce SIDS risk by following safe sleep guidelines:
- Always place an infant on his or her back to sleep
- Ensure an infant has a firm sleep surface - such as a mattress - covered with a fitted sheet and placed inside a safety-approved crib
- Avoid use of pillows, blankets, sheepskins or crib bumpers in a baby's sleep area - these can increase risk of suffocation
- Ensure nothing is covering an infant's head - avoid using blankets
- Ensure an infant is dressed in appropriate clothing to sleep - such as a one-piece
- Do not bed-share with an infant
- Keep toys, soft objects and loose bedding out of an infant's sleep area
- Avoid smoking around an infant.
The researchers stress, however, that the absolute risk of SIDS is very low for infants at high altitude, and that their findings do not call for parents to move from high-altitude areas or to avoid trips to areas of high altitude.
The team concludes that further research is warranted to determine exactly what drives the association between high altitude and increased risk of SIDS.
In October 2014, a Spotlight feature from MNT investigated the risks and benefits of bed-sharing with infants.