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Am Fam Physician. 2008;77(9):1312-1315

Background: Smoke-free legislation has been advocated as a strategy to reduce secondhand smoke exposure and hence reduce tobacco-related morbidity. However, there are concerns that an unintended consequence of smoke-free legislation could be increased smoking in the home, resulting in a paradoxical increase in secondhand smoke exposure, especially for children. Akhtar and colleagues studied the impact on schoolchildren of legislation introduced in March 2006 that banned smoking in most enclosed public places in Scotland.

The Study: The study used two school-based surveys (one in January 2006 and one in January 2007) of a representative sample of Scottish children (mean age of 11.4 years). The 2,559 participating children completed a questionnaire that included questions about their own smoking and that of their friends and parents. The survey also addressed their exposure to tobacco smoke outside of the home. A group of 2,424 children completed the same survey in 2007. All participants were asked for a saliva sample to test for cotinine levels. Participants with high cotinine levels (i.e., greater than 15 ng per mL [85.0 nmol per L]) were excluded as being active smokers. Differences in cotinine levels between the two surveys were measured and linear regression analyses were used to adjust for age, family social status, and number of parental figures who smoked.

Results: The distribution of sex, family structure, and socioeconomic status of participants did not differ significantly in the two surveys. After legislation, the median cotinine concentration fell from 0.3 to 0.2 ng per mL (2.0 to 1.0 nmol per L) and the percentage of pupils with undetectable levels rose from 20 to 34 percent. The authors calculated a 39 percent drop in adjusted mean cotinine concentration. Exposure to smoking in the two most common sites (i.e., home and car), as reported by the children, did not differ between the two surveys. The percentage reporting at home was 27.8 and 27.4 percent, respectively. For exposure in cars, the percentages were 6.7 and 6.5, respectively. Reported exposure in restaurants or cafes fell significantly (from 3.2 to 0.9 percent), as did exposure on public transportation (from 1.5 to 0.6 percent). A significantly lower proportion of children also reported a significant decrease in exposure in homes other than their own (from 11.6 to 9.5 percent).

In each survey, more than 40 percent of children lived with a parent who smoked. The mean cotinine levels increased significantly with the number of parents smoking at home, from 0.14 ng per mL in the 2006 survey and 0.07 ng per mL in the 2007 survey in children with nonsmoking parents to 1.94 and 1.74 ng per mL in the same surveys for children with two parental figures who smoked at home. In children with at least one parent who smoked, the study detected a fall in mean cotinine concentration of 44 percent if only the father smoked, but only 11 percent in those children if the mother or both parents smoked.

Conclusion: The authors conclude that smoke-free legislation was associated with significant reductions in secondhand smoke exposure in children. The greatest benefits appeared to be for children living in smoke-free households. No evidence was found of increased smoking at home following restrictions on smoking in public places.

editor's note: A related study of more than 1,800 Scottish adults (18 to 74 years) also showed an overall reduction of 39 percent in mean saliva cotinine concentrations of non-smokers, with the greatest reductions (49 percent) in non-smokers living in nonsmoking households, and non-statistically significant declines (16 percent) in non-smokers living with one or more smokers.1

An accompanying qualitative study2 of 50 adults and an editorial3 illustrate how attitudes and social pressures are changing regarding smoking. Passive smoking is widely accepted as a serious health issue, especially for children. The traditional attitude that adults have an unrestricted “freedom to smoke”, especially in one's own home and car, appears to be increasingly challenged by social pressures and formal restrictions. Two key social values are emerging in this debate: being hospitable to all, including smokers; and being a caring parent or grandparent of a child by protecting them from smoke exposure.

The bottom line appears to be that legislation contributes to reducing the adverse health effects of tobacco smoke, and that bans on smoking in public places do not displace passive smoke exposure in the home. However, the greatest future gains in reducing tobacco smoke may be from social action through normative attitudes and behaviors, and formal regulation. Both presently appear to be working against tobacco, but the current patterns of smoking by adolescents and young adults, particularly young women, could indicate future difficulties for this momentum toward significant social change.—a.d.w.

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