|The Sudden Infant Death Syndrome Alliance||1314 Bedford Avenue
Baltimore, MD 21208
TO: Affiliate Presidents and Executive Directors
FROM: Phipps Cohe, National Public Affairs Director
RE: New British Meta-Anaylysis Reaffirms That Maternal Cigarette Smoking Doubles The Risk Of SIDS
Scheduled to coincide with national No Smoking Day in Great Britain, a meta-analysis of existing data available on cigarette smoking and SIDS risk was published and its findings released to the British media on March 11, 1998. This review of the epidemiological evidence linking maternal smoking and SIDS was based on 39 studies, incorporating a number of major recent studies and including some earlier studies not mentioned in existing reviews. It was conducted by scientific investigators at the Department of Public Health Sciences, St. George's Hospital Medical School, in London, and was completed in April 1997. The authors, H. Ross Anderson and Derek G. Cook, conclude that "maternal smoking doubles the risk of Sudden Infant Death Syndrome." They further conclude that "the relationship is almost certainly causal."
Though it is considered to be one of the most significant known risk factors for SIDS, medical experts in the U.S. stop short of describing the association between cigarette smoke exposure and SIDS as "causal." Case control, population-based studies from several countries have shown that cigarette smoking during pregnancy triples the risk for SIDS. Epidemiologic studies have shown that exposure to cigarette smoke in the environment after birth doubles the risk for SIDS. These studies have led some scientists to believe that cigarette smoking is part of the causal pathway, possibly due to intrauterine hypoxia, although the mechanism is still not clear.
Some recent studies have added to our understanding of the possible physiologic mechanisms underlying the association between smoking and SIDS. Scientists (Kinney et. al.) have documented defects in some SIDS infants in sites of the brainstem involved in arousal, heart and breathing functions, sleep, and body movement control. While we do not yet know exactly how smoking affects a fetus, abnormalities in the developing nervous system have been observed in animals exposed to cigarette smoke in utero.
Components of smoke are also believed to have a negative effect on fetal lung development. Based on epidemiologic investigations, sustained cigarette smoke exposure makes it more difficult for babies who are already vulnerable to breathe. In addition, smoke exposure may disrupt the arousal mechanism in infants, as it is known to do in adult smokers, and may contribute to neonatal death during an hypoxic episode. Moreover, its effect on narrowing blood vessels induces smokers to keep their environments warmer and to use more bedding than non-smokers--two more factors that increase the risk of SIDS.
Studies have also shown that infants who share a bed with smokers may be subjected to higher levels of smoke than other infants because of more and closer contact with the smokers (Mitchell et. al.). Recent attention to the potential relationship between particulate air pollution and SIDS (Woodruff et. al.) has raised scientific speculation regarding possible harmful components of cigarette smoke beyond nicotine.
In Great Britain, where prone sleeping is no longer a major SIDS risk factor due to the success of the "Back To Sleep" public health campaigns, cigarette smoking has emerged as the main risk factor for SIDS. The Confidential Enquiry into Stillbirths and Deaths in Infancy (Fleming, et. al.) found the risk of SIDS to rise with increases in the numbers of smokers in the household, the number of cigarettes smoked a day, and the length of exposure to cigarette smoke. The study concluded that it should be considered "as anti-social to smoke around an infant as it is to drink and drive."
As the body of evidence against infant exposure to cigarette smoke continues to mount, parents are strongly advised not to smoke during pregnancy and the critical first year of development, or allow anyone else to smoke around the baby either. It is equally important that, since many babies still die of SIDS in smoke-free environments and since the cause(s) of SIDS remain unknown, SIDS parents refrain from concluding that their childcare practices may have caused their baby's death. Further research is needed to explain and eliminate Sudden Infant Death Syndrome.
1.) Though a direct causal relationship has not been established, prenatal and postnatal exposure to cigarette smoke have repeatedly been identified as significant risk factors for SIDS.
2.) In accordance with the "Back To Sleep" public health message, the SIDS Alliance continues to urge new parents and all those who care for infants to position babies on their backs for sleep; provide a smoke-free environment; use firm bedding materials; avoid overheating; breastfeed to build immunity; maintain good prenatal care, regular immunization schedules, and communication with your baby's doctor regarding any changes in health and behavior.
3.) Avoiding cigarette smoke is a recognized approach to reducing the risk of SIDS. However, it is important to refrain from making smoke exposure appear to be linked to all SIDS deaths. Many SIDS deaths occur in a smoke-free environment and many babies exposed to cigarette smoke do not die.
4.) The cause(s) of SIDS remain unknown, and it is possible that SIDS may have a number of causes, not just one. We cannot predict which babies will die, nor can we prevent all SIDS deaths. Therefore, we must continue to support medical research efforts aimed at uncovering additional risk factors and underlying causes.
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