Smoking Ban linked to reduced Asthma

The ban on smoking in public places in England has been linked to a 4.9% reduction in hospital admissions for adult asthma, according to research published in the journal Thorax.

Smoke free legislation was introduced in England in 2007, banning smoking in enclosed public places.  As second-hand smoke is known to have deleterious effects on the adult respiratory system, and previous research suggests it contributes to the onset of acute asthma attacks and to poorer outcomes in asthma patients.  The prevalence of asthma in England is amongst the highest in the world, with approximately 5.9% of the population diagnosed.

Other biomarkers already suggest that exposure to second hand smoke is reducing since the ban, but Michelle Sims at the University of Bath and colleagues wanted to see if the smoking ban could be empirically associated with an immediate reduction in emergency hospital admissions for asthma in the adult population.

To find out, they collated monthly numbers of adult emergency admissions from April 1997 to December 2010 where the primary diagnosis had been asthma.  This was then controlled for size of population, seasonal variation in asthma cases and to exclude long term trends.

Previous research, conducted in Ireland, Kentucky, Delaware and New Zealand, show widely different results, from a 5% reduction in admissions through to a whopping 40% reduction, so key to this research was to iron out bias and statistical error that could lead to such differing results.

To do this, they took into account monthly mean temperatures for each region, cases of influenza, changes in population over time, age & gender distribution and a host of other factors.  They then looked at each region independently and as part of a model covering all of England.

They concluded that there was an immediate reduction in admissions of 4.9%, implying that approximately 1900 admissions were prevented in each of the first three years after the ban.

Although correlation does not imply causation, and it would be very tricky to conclusively show that the smoking ban is responsible for the drop in admissions, the authors conclude:

"[This] adds to the expanding body of evidence that smokefree policies are associated with positive health outcomes." And call for further research in other geographical areas.