This is the first study to examine the relationship between coverage by state and local smoke‐free laws and an objective measure of SHS exposure in a national survey. Our findings indicate that there was a significant association between the level of coverage and SHS exposure. Tobacco‐free adults without home SHS exposure living in areas with county‐wide coverage by at least one smoke‐free workplace, restaurant, or bar law consistently had a lower prevalence of SHS exposure than adults residing in counties without a smoke‐free law. Our results showed that there was up to a 90% reduction in the odds of SHS exposure for adults residing in counties with extensive coverage compared to those without smoke‐free policies. Specifically, men in counties covered by at least one smoke‐free law had one tenth the odds and women had one fifth the odds of being exposed to SHS, compared with men and women residing in areas not governed by a smoke‐free law. The strength of the associations in both men and women provides evidence of the beneficial effects of smoke‐free laws in the US population.
We used gender‐stratified logistic regression models because of the interaction effect between gender and smoke‐free law coverage categories. The prevalence of SHS exposure among men and women was similar living in areas with extensive coverage, suggesting that smoking restrictions may protect both men and women equally. However, men had higher SHS exposure than women in the limited and non‐coverage areas. A possible reason for this difference is that men may work in or frequent establishments that allow smoking more often than women. We do not have additional exposure information in NHANES to explore this issue further.
For all non‐smoking adults, education (less than or equal to a high school education) and age (20–39 years) were associated with an increased likelihood of SHS exposure. This is consistent with patterns of cigarette smoking among adults. Adults with less than a high school diploma typically are more likely to be employed in blue collar or service worker jobs, and less likely to be protected by a smoke‐free policy than white collar workers.26,27
Non‐smoking adults in our study may be exposed to SHS through demographically similar peer groups.
In our multivariate analysis, non‐Hispanic blacks were up to three times more likely to be exposed to SHS than non‐Hispanic whites. Previous studies have shown that non‐Hispanic blacks have higher cotinine levels than non‐Hispanic whites in non‐smokers20,28
as well as smokers.29,30,31
The studies of smokers have suggested that differences may be due to nicotine metabolism or clearance, type of cigarette smoked (mentholated or non‐filter) and patterns of smoking behaviour.29,30,32
Although there was a smaller proportion of non‐Hispanic blacks in counties with extensive coverage compared to the other coverage groups, this was controlled for in the multivariate analyses.
Limitations of our study should be noted. Because the smoke‐free law classification scheme is not part of the sample design of NHANES, the primary sampling units (counties) selected during the four years of the survey may not be statistically efficient with respect to representation of all US counties within each coverage category. Estimates for smoke‐free law coverage groups may have differed if the counties were selected to be specifically representative of these categories.
Another limitation is that individual risk of exposure to SHS may not be captured by the three smoke‐free law coverage categories in our analysis. Individual workplaces and restaurants may have more restrictive voluntary policies than their respective local or state laws. For example, participants classified as residing in a county with no coverage may have potentially worked in a 100% smoke‐free building, and this may explain the low proportions of adults who reported work SHS exposure (9.3%) in counties with no smoke‐free laws. Likewise, counties with extensive smoke‐free law coverage were not uniform with respect to the type of location covered. Specifically, all of the counties had a smoke‐free restaurant law, but not all counties had bar or workplace laws. Also, we did not take into account adults who worked or spent time outside their county or state of residence and may have been subjected to a different set of tobacco control laws. Lastly, we focused on smoke‐free laws and did not consider less restrictive ordinances,33
which, nevertheless, provide some protection from SHS exposure in public places and worksites.
In our survey we found that the prevalence of current smoking among all adults varied by level of law coverage. In counties with extensive, limited and no smoke‐free law coverage, the prevalence of smoking was 17.2% (95% CI 13.6% to 21.6%), 16.7% (95% CI 12.4% to 22.1%), and 26.6% (95% CI 24.7% to 28.5%), respectively. Research suggests that strong smoke‐free laws may contribute to reductions in smoking prevalence.1,8,34,35,36
Due to the cross‐sectional design of the survey, we could not determine whether smoke‐free laws help reduce smoking prevalence or whether smoke‐free laws were more likely to be implemented in areas with lower smoking rates. We also cannot rule out the possibility that less second hand smoke exposure occurs in places with extensive coverage because there are fewer smokers in these areas.
What this paper adds
Several studies have shown reduced levels of secondhand smoke (SHS) in public places after implementation of a smoke‐free law. These studies have focused on policies specific to state, city, or workplace laws, and have most often measured SHS exposure using self‐reported or environmentally monitored data.
This is the first study to look at the relationship between smoke‐free laws and SHS exposure in a national population using a direct measure of SHS exposure, serum cotinine. We found a strong inverse association between smoke‐free law coverage and SHS exposure. This study adds a new perspective to the body of evidence showing that persons who live in areas with smoke‐free laws have lower SHS exposure than persons not protected by these regulations.
Despite these limitations, our results are consistent with previous studies comparing SHS levels in localities before and after the implementation of smoke‐free laws. In California, self‐reported SHS exposure among bartenders showed a reduction of about 93% in the median hours of exposure.11
New York and Delaware both saw reductions in respirable suspended particles in hospitality venues of 84% and 90%, respectively, after state laws required all indoor workplaces and public places to be smoke‐free.13,14
In the Republic of Ireland, after legislation of smoke‐free workplaces and bars was enacted, salivary cotinine levels declined by 80% among bar staff.37
Other studies show that not only do smoke‐free laws reduce SHS exposure, but that they improve the respiratory and cardiovascular health of populations as well. Eisner et al
found that after smoking was banned in bars and taverns in California in 1998, there was a rapid improvement in respiratory health among bartenders.11
During a six month period that a smoke‐free workplace law was in effect in Helena, Montana, hospital admissions for acute myocardial infarction decreased by 40% and returned to previous levels after the ordinance was suspended.12
Farrelly and colleagues showed a decline in salivary cotinine, as well as in sensory symptoms among hospitality workers one year after the implementation of New York's smoke‐free laws.15
Declines in respiratory symptoms were also reported among bar staff in the Republic of Ireland and in Norway after the implementation of smoke‐free laws.37,38,39
Smoking bans and restrictions as a means to reduce exposure to SHS and prevent significant morbidity and mortality are based on strong scientific evidence.1,40
Our results enhance earlier findings that smoke‐free laws are an effective strategy for reducing SHS exposure. Over the past 10 years, we have seen a marked increase in smoke‐free laws at the state and local levels in the United States, as well as in other countries.17,33,41
When cotinine levels were first measured in NHANES (1988–91) 90% of non‐smokers had detectable levels of cotinine,20
and less than 1% of the US population was covered by a smoke‐free worksite, restaurant, or bar law.42
By 2002, approximately 15% of the population was covered by a smoke‐free law (L Williams, ANRF, personal communication), and according to the 1999‐2002 NHANES, only 43.4% had detectable cotinine levels. It is encouraging to note that by 2006, 39% of Americans are protected by a state or local smoke‐free law.17