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Objective--To examine the importance of parental smoking on passive exposure to tobacco smoke in children and the social and geographical patterns of exposure.
Design--Cross sectional study.
Setting--Schools in 10 towns in England and Wales; five towns with high adult cardiovascular mortality and five with low rates.
Subjects--4043 children aged 5-7 years of European origin.
Main outcome measures-Salivary cotinine concentration and parents self reported smoking habits.
Results--1061 (53.0%) children were exposed to cigarette smoke at home or by an outside carer. Geometric mean cotinine rose from 0.29 (95% confidence interval 0.28 to 0.31) ng/ml in children with no identified exposure to 4.05 (3.71 to 4.42) ng/ml in households where both parents smoked and 9.03 (6.73 to 12.10) ng/ml if both parents smoked more than 20 cigarettes a day. The effect of mothers' smoking was greater than that of fathers', especially at high levels of consumption. After adjustment for known exposures geometric mean cotinine concentrations rose from 0.52 ng/ml in social class I to 1.36 ng/ml in social class V (P [less than] 0.0001); and were doubled in high mortality towns compared with the low mortality towns (P = 0.002). In children with no identified exposure similar trends by social class and town were observed and the cotinine concentrations correlated with the prevalence of parental smoking, both between towns (r = 0.69, P = 0.02) and between schools within towns (r = 0.50, P [less than] 0.001).
Conclusions--Mothers' smoking is more important that fathers' despite the lower levels of smoking by mothers. Children not exposed at home had low cotinine concentration, the level depending on the prevalence of smoking in the community.
In the past decade many studies have investigated the health effects of passive exposure to tobacco smoke in non-smoking children. Most studies have relied on questionnaire measures of parental smoking as the indicator of exposure. Such measures ignore exposure by people from outside the household, the extent to which parents smoke in the presence of the child, and other modifying factors such as the ventilation of the room. These studies may therefore have underestimated the real effect of passive smoking in children. Biochemical measures allow recent exposure to be estimated directly.
Cotinine, a metabolite of nicotine, is the best biochemical marker for quantifying passive exposure to smoke. It is specific to tobacco, has a half life of about 20 hours, and can be detected at low concentrations by gas-liquid chromatography. Salivary concentrations are in approximate equilibrium with those in the blood and provide a noninvasive way of measuring passive smoke exposure. We present an analysis of the relation between cotinine concentration and questionnaire data in children aged 5-7 from 10 towns in England and Wales. We examine the importance of parental exposure as opposed to other sources; exposure among children from non-smoking households; and the social and geographical pattern of passive exposure to tobacco smoke in children.
Subjects and methods
The study was carried out in 10 towns in England and Wales--five with high adult cardiovascular mortality (Wigan, Burnley, Rochdale, Port Talbot, and Rhondda) and five with low mortality (Esher, Leatherhead, Chelmsford, Bath, and Tunbridge Wells). The selection of these towns has been described in detail. Because of the strong geographical association between mortality from cardiovascular disease and that from respiratory disease, this resulted in five towns with high mortality from respiratory diseases and five with low mortality. Within each town we selected a sample of 10 primary schools stratified by religious denomination and, in the case of county primary schools, by size and location. Any school unable to take part was replaced by the school that matched most …