NATIONAL BUREAU OF ECONOMIC RESEARCH
NATIONAL BUREAU OF ECONOMIC RESEARCH

Cigarette Regulations Reduce Cases of Sudden Infant Death Syndrome

"More stringent cigarette regulations have a distinct and direct impact in reducing SIDS deaths. The largest reduction in deaths comes from changes in the monetary price of cigarettes. Each 10 percent increase in the real price of cigarettes reduces the average number of SIDS deaths by a range of 6.7 to 7.4 percent."

Sudden Infant Death Syndrome (SIDS) is the unexplained, sudden death of an infant under one year of age. SIDS is the leading cause of mortality among infants aged 1-12 months, and is responsible for thousands of infant deaths every year, according to the Centers for Disease Control (CDC). Rates of SIDS in the United States have been declining steadily since 1980, from 1.53 per 1000 live births to 0.53 per 1000 live births in 2003. But the difficulty in identifying the causes of SIDS makes it difficult to attribute the reasons for the decline. The "Back to Sleep" campaign, which recommends that infants should be put to sleep in a supine position, has been widely cited for achieving significant reductions in SIDS in the United States. However, given that this campaign began in the mid-1990s, there is still much unknown about the trends, causes, and prevention of this syndrome.

Much of the current research on SIDS focuses on identifying the risk factors that are consistently observed to be associated with elevated risks of SIDS. The CDC summarizes seven primary risk factors: 1) tummy or side sleeping; 2) soft sleep surfaces; 3) loose bedding; 4) overheating; 5) smoking; 6) bed sharing; and 7) preterm and low birth weight. For many of these risk factors, public education campaigns may be the only way to encourage the behaviors that will reduce SIDS. However, for smoking, the policymakers have a variety of tools to use besides public education. Cigarette taxes and laws regulating indoor smoking are known to be strong predictors of smoking behaviors among all adults and pregnant women. If smoking is truly a causal determinant of SIDS, then policies that reduce smoking should have the added benefit of reducing SIDS cases.

In The Effectiveness of Cigarette Regulations in Reducing Cases of Sudden Infant Death Syndrome (NBER Working Paper No. 12527), author Sara Markowitz examines the direct effects of changes in cigarette prices, cigarette taxes, and clean indoor air laws in explaining changes in the incidence of SIDS over time in the United States. She takes a new approach to studying the prevention of SIDS by combining the lessons from epidemiology and economics. Epidemiological studies have shown that prenatal maternal smoking and postnatal environmental smoke are major risk factors for SIDS deaths. Research in economics has shown that smoking is influenced by the determinants of the demand for cigarettes, including the monetary price and restrictions on smoking in public places. By combining these two relationships, Markowitz shows that more stringent cigarette regulations have a distinct and direct impact in reducing SIDS deaths.

The largest reduction in deaths comes from changes in the monetary price of cigarettes. Each 10 percent increase in the real price of cigarettes reduces the average number of SIDS deaths by a range of 6.7 to 7.4 percent. A 10 percent increase in the real taxes on cigarettes reduces SIDS deaths by a range of 1.56 to 1.79 percent. The difference in the magnitude of the price and tax effects is not surprising, since taxes make up only a portion of cigarette prices.

Restrictions on smoking in public places also may save babies' lives. Markowitz finds that each additional restriction placed on smoking decreases the average quarterly SIDS count by 0.92 for private workplace restrictions, by 1.2 for restaurant restrictions, and by 0.39 for child care center restrictions. The effectiveness of higher cigarette prices and taxes and more stringent restrictions on smoking in public places holds whether these factors are evaluated contemporaneously with the SIDS cases, or lagged one year to represent the policies that existed during the prenatal period.

While this study sheds light on the relationship between smoking and SIDS, a number of studies, from the United States and other countries around the world, have established both prenatal and postnatal smoking as major preventable risk factors for SIDS. One comprehensive review of the literature found that maternal smoking doubles the risk of SIDS. A 2006 U.S. Surgeon General's report on the Health Consequences of Involuntary Exposure to Tobacco Smoke concurred that the evidence was "...sufficient to infer a causal relationship between exposure to secondhand smoke and sudden infant death syndrome."

Postnatal smoking by either the mother or other household members also has been shown to be a risk factor for SIDS. Many studies have found a positive relationship between postnatal smoking and SIDS, even after controlling for other risk factors such as maternal characteristics, prenatal smoking, and, in some studies, sleep position. The risk of death is also found to rise with increasing levels of smoking. One meta-analysis of postnatal maternal smoking found that smoking after pregnancy increases the risk of SIDS by 94 percent.

Smoking by fathers and other household members is also believed to be associated with an increased risk of SIDS, although the evidence is not consistent across studies. These studies are all case-controlled, matching families of infants who died to a sample of control families with similar characteristics. Many studies are population based, but often have small sample sizes and focus on restricted geographic areas.

The results of this paper contribute to the evidence for the causal relationship between smoking and SIDS, while avoiding the potential biased caused by omitted unobserved variables. The findings that higher cigarette prices and stricter clean indoor air policies reduces SIDS are consistent with the theory that smoking causes SIDS.

-- Les Picker

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