Research articleRestrictions on smoking at home and urinary cotinine levels among children with asthma
Introduction
T here is good evidence from epidemiologic studies that exposure to environmental tobacco smoke (ETS) is associated with new cases of childhood asthma and poorer symptom control among children with existing asthma,1 higher rates of hospital utilization,2 and slower rates of recovery after exacerbation.3 Children with asthma who have parents who smoke are likely to have high levels of ETS exposure. While the recommendation to parents of children with asthma is that they should quit smoking, the reality is that many are not able to.4 For this reason, parents have been encouraged to ban smoking in the home as a way of reducing exposure to ETS. However, it has been unclear from the published literature whether even more intermediate restrictions on smoking in the home offer protection from ETS. These harm-reduction strategies for reducing exposure of children to ETS have been identified as a priority for research.5
Cotinine, as a metabolite of nicotine, is recommended as a valid quantitative measure of exposure to ETS.6, 7, 8 The ratio of cotinine to creatinine in urine adjusts for fluid volume to overcome dilution.9, 10 In one study of children aged <14 years in Greece, cotinine to creatinine ratios (CCRs) decreased by 38% when precautions were taken to limit exposure of children to ETS (defined as not smoking in the presence of the child, smoking only in restricted home areas, or regularly opening windows to freshen indoor air).11 However, precautions were examined as a single category and not disaggregated. Another study in Baltimore found smoking outside the home to be the only modification to smoking practices associated with reduced urinary CCRs.12
Studies in indoor environments suggest that nicotine levels decline with greater distance from the smoker.13, 14 This implies that there may be some benefit in reducing exposure of children to ETS, even for practices that do not involve complete bans on smoking in the home. Clearly, factors such as the size, layout, and ventilation of the home will influence nicotine concentrations in the air, 15, 16 but the question remains as to whether only total bans substantially lower exposure to ETS or whether there are declines associated with less restrictive practices. This study sought to determine the extent to which different types of restrictions on smoking in the home were related to urinary cotinine levels among children with asthma.
Section snippets
Methods
The data used in this study were part of a randomized controlled trial of a smoking change intervention for parents of children with asthma. Study subjects included children aged between 1 and 11 years with doctor-confirmed asthma who attended pediatric outpatient clinics of two major metropolitan hospitals in Adelaide, South Australia, during the period July 1998 to March 1999. To be eligible for the study, the child needed to have at least one English-speaking parent who was a smoker.
Where
Results
Three cases were identified as outliers, having standardized scores >3.29 (167 nmol/mmol),21 leaving 249 cases available for analysis. The mean age of the children was 5.5 years (standard deviation [SD]=2.9) and 65.5% were boys. CCR values were skewed (2.11) and ranged from 0.5 nmol/mmol to 149.0 nmol/mmol with an arithmetic mean of 24.6 nmol/mmol (SD=28.0). Transformation using logarithm e resulted in a more normal distribution with skewness of −0.34 and a geometric mean of 13.0 nmol/mmol
Discussion
This study found that where exceptions to home-smoking bans were made, whatever these exceptions were, children’s urinary CCR levels were no different to homes where smoking was only allowed in rooms where the child rarely frequented. These two intermediate levels of restriction were in turn associated with significantly greater CCR levels than a total ban on smoking with no exceptions of any kind, and significantly lower CCR levels than unrestricted smoking in common rooms of the home.
There
Acknowledgements
This study was funded by the Australian National Health and Medical Research Council (grant number 980608). The authors wish to acknowledge the assistance of Else Jansen and Ingerid Meagher in collecting the data, Heather Katzenberg for assistance with CCR analysis, Lyn Roberts for early input into the study design, the staff of outpatients clinics at the Women’s and Children’s Hospital and the Lyell McEwin Health Service, and the parents and children who gave of their time to be involved in
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