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Re: ETS and asthma: U shaped effect? - Author's response

Dr McFadden is putting forward an interpretation of the small non- significant decrease in asthma episode contacts seen amongst those with moderate exposure to passive smoking. In our view this is unwise. The effect could well be due simply to the play of chance. Further we have shown that non-clinical factors have a dominant influence on visit frequency and that the frequency of contacts is a poor measure of asthma morbidity. In consequence our study gives no support at all to the idea that moderate levels of tobacco smoke suppress asthma. We agree that further research is needed both into the consequences of passive smoking and also into the determinants of health care utilisation among children with asthma.

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Re: ETS and asthma: U shaped effect?

If the abstract indicates correctly that children of totally non-smoking parents were not included in the study, I see that as a significant weakness.

The study found, as might be expected by many, an increase in contacts for asthma episodes among children most heavily exposed to environmental tobacco smoke (ETS).

However, it also found a non-significant but noteworthy decrease in asthma episode contacts among those with "moderate" exposure as opposed to "low" exposure. If non-smoking parents (which would presumably usually have children with *extremely* low exposure) had been included as a study group as well, we might have seen a continuation of the U-shaped curve indicating support for the idea that moderate levels of tobacco smoke in the air might act in some way as a suppressor to asthma or asthma episodes among children regularly exposed to such. Such a finding would also be in line with the observed increase in asthma among American children over the last few decades that seems to form a strikingly inverse relationship with the exposure of American children to secondary smoke in the home and such venues as fast-food restaurants and child care facilities.