Public Smoking Ban and Childhood Asthma

William T. Basco, Jr., MD


December 07, 2010

Smoke-free Legislation and Hospitalizations for Childhood Asthma

Mackay D, Haw S, Ayres JG, Fischbacher C, Pell JP
N Engl J Med. 2010;363:1139-1145

Study Summary

Mackay and colleagues explain that 25% of adults in Scotland smoke tobacco products, but most child exposure to tobacco smoke is environmental, primarily from household contacts. Two earlier studies found that 40% of children live with at least 1 adult who smokes.[1,2] In 2006, Scotland enacted a smoking ban on all enclosed public spaces and workplaces, including pubs. Previous studies documented a reduction in respiratory symptoms in pub workers following the ban, and it has also been associated with an increase in families' adoption of in-home smoking bans.

This study sought to examine pediatric admissions to hospitals over the period before and after the smoking ban to determine if the ban was associated with reduced asthma morbidity and mortality among children. The investigators used Scottish national administrative records to identify admissions to hospitals and combined these data with a death certificate registry. The study period covered January 2000 through October 2009. The hospitalizations analyzed included those with asthma as a primary diagnosis, but the investigators added prehospital deaths from asthma to create an "asthma events" outcome (admissions + prehospital deaths from asthma). The analyses also accounted for age (0-4 years vs 5-14 years), socioeconomic status (in quintiles), and whether the child lived in an urban vs rural area. The denominators used for calculations were the 2001 census figures for Scotland. The study period included 21,415 admissions for asthma in children who met study criteria.

The researchers noted that from approximately mid-2002 until January 2006 (onset of smoking ban), asthma admissions were increasing in the study population by about 5% per year. However, after the ban went into effect, there was an 18% reduction in the annual rate relative to the 2006 peak; additionally, admission prevalence was less than the annual rate from 2000. Overall, asthma admissions were 13% lower (95% confidence interval, 10.4-15.6) after implementation of the ban. The estimated reduction was actually greater after controlling for sex, age, location of residence, and economic stratum, at approximately 15% per year. No differential effects were observed for any subgroup. With only 5 asthma deaths in the study age group during the period studied, evaluation of asthma admissions + prehospital asthma deaths did not change the overall findings. There was no regional variation in the findings. The investigators concluded that the implementation of a ban on smoking in public places in Scotland was associated with a subsequent decline in hospitalizations for asthma in children.


The investigators acknowledged that they had only population-level data and were therefore unable to examine the potential smoke exposure of any specific patient with an asthma hospitalization. However, the findings and conclusions of this "natural experiment" are strengthened by the fact that the association has biologic plausibility and a strong temporal association. A similar population-based analysis demonstrated a reduction in asthma episodes during the 1996 Atlanta, US Olympics when daily commuting was reduced and air quality improved.[3] These data serve as a reminder to practitioners to inquire about environmental exposures among patients with asthma, especially if the patient seems to have difficulty reaching adequate control.



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