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Air Pollution Linked to Higher SIDS Risk

Sulfur Dioxide, Nitrogen Dioxide, and Carbon Monoxide Among Pollutants Listed

WebMD Health News

June 7, 2004 -- Air pollution may play a role in increasing the risk of sudden infant death syndrome (SIDS), according to a new study.

SIDS strikes about one in every 1,000 babies, and the exact cause of the mysterious condition is unknown.

Researchers say the role of air pollution in SIDS is controversial, and few studies have looked at the relationship between the two because of difficulties in creating a study that can control for environmental factors and ethical issues relating to exposing human infants to risk relating to death as an outcome.

But this study, published in the June issue of Pediatrics, shows daily increases in two common air pollutants are associated with a nearly 18% increase in SIDS rates.

Air Pollution May Affect SIDS Risk

In the study, researchers looked at daily air pollution concentrations in 12 Canadian cities from 1984 to 1999 and compared them with daily SIDS rates.

They found increased SIDS rates were linked to increases in the previous day's air pollution concentration of sulfur dioxide. They also found that other pollutants such as nitrogen dioxide and carbon monoxide were also linked to an increase in SIDS rates. Researchers found the link to nitrogen dioxide and carbon monoxide and SIDS deaths when they averaged the levels of these pollutants in the three days preceding a death.

These effects remained significant after controlling for weather (either season alone or the combination of average daily temperature, relative humidity, and changes in barometric pressure), sulfur dioxide, and nitrogen dioxide -- but not carbon monoxide.

Increases in both sulfur dioxide and nitrogen dioxide were associated with a 17.7% increase in SIDS rates.

No association was found between ozone or fine particle levels, but researchers this may have been because these air pollutants were measured only every sixth day.

Researchers say several factors might explain the possible causal link between air pollution and SIDS found in this study:

  • Air pollution is associated with increases in heart- and lung-related deaths and SIDS is the result of when the heart and lungs shut down.
  • Environmental exposure to tobacco smoke has already been shown to increase the risk of SIDS.
  • Sulfur dioxide and nitrogen dioxide have been associated with low birth weight, which increases the risk of infant death.
  • Sulfur dioxide is a highly water-soluble gas that is absorbed into and irritates the upper respiratory tract.

Although more research is needed to better understand the link between air pollution and SIDS, other widely recognized risk factors for SIDS include:

  • The winter season and overheating an infant with too many layers while he or she sleeps
  • Putting an infant to sleep on his or her stomach or side
  • Exposing infants to tobacco smoke
  • Lower social status of parents

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