Does tobacco smoke prevent atopic disorders?: A study of two generations of Swedish residents

Background Earlier studies have given conflicting results regarding the effect of exposure to tobacco smoke on atopic sensibilization. Methods A cross-sectional study of present and former smoking habits in relation to atopic disorders from data on 6909 young and middle-aged adults (16-49 years) and their 4472 children (3-15 years) from the Swedish Survey of Living Conditions in 1996-97. Results The prevalence of allergic asthma and allergic rhino-conjunctivitis decreased, in a dose-response manner (P = 0.03 and P = 0.004, respectively), with increasing exposure to tobacco smoke in the adult study population. This pattern was little changed when potential confounders (sex, age, education, domicile, country of birth) were entered into a multivariate analysis: the adjusted odds ratio (OR) for allergic rhino-conjunctivitis was 0.5 (0.4-0.7) for those who smoked at least 20 cigarettes a day and OR 0.7 (0.6-0.9) for those smoking 10-19 cigarettes, compared with those who reported that they never had smoked Former smokers had a tendency for a slightly lower risk: OR 0.9 (0.8-1.0). In a multivariate analysis, children of mothers who smoked at least 15 cigarettes a day tended to have lower odds for suffering from allergic rhino-conjunctivitis, allergic asthma, atopic eczema and food allergy, compared to children of mothers who had never smoked (ORs 0.6-0.7). Children of fathers who had smoked at least 15 cigarettes a day had a similar tendency (ORs 0.7-0.9). Conclusions This study demonstrates an association between current exposure to tobacco smoke and a low risk for atopic disorders in smokers themselves and a similar tendency in their children. There is a need for further studies with a prospective design to certify the causal direction of this association. Smoking habits and atopic disorder in parents should not be considered independent variables in epidemiological studies of the connection between exposure to tobacco smoke and atopy in children.