Smoking bans may have reduced premature births and asthma emergencies

Passive smoking

We’re still mining a rich seam of evidence summaries from the latest Eyes on Evidence.  The same issue that looked at how to encourage poorer women to be more physically active also contains an evidence summary on the impact of smoke-free legislation on population health.

The summary focuses on the impact of passive smoking, and resultant health gains from reducing non-smokers’ exposure to tobacco smoke in areas that have been subject to a ban.

The article also summarises the estimated impact of passive smoking and the findings from  other early studies showing that smoking bans have reduced the incidence of diseases associated with second-hand smoke around the world.

Background

Some smokers of yesteryear

The evidence is pretty consistent that eliminating passive exposure to smoke signficiantly improves the health of non-smokers

The Lifestyle Elf has traditionally had a strong focus on research that looks at how we can help people to kick the baccy.  Smoking affects so many health outcomes that there is a very diverse array of studies underway to look at the impact of smoking bans.

This Eyes on Evidence summary looks at two observational studies:

  1. the impact of smoking bans on pregnancy outcomes
  2. the impact of smoking bans on emergency hospital admissions for asthma.

The evidence

The first study found that smoking bans were associated with a reduction in premature delivery

The first study found that smoking bans were associated with a reduction in premature delivery

The first study looked at all 448,520 spontaneous births in Belgium during a ten-year period that spanned the introduction of three different smoking bans.  The researchers observed statistically signficiant reductions in the percentage of pre-term births after the introduction of each smoking ban.

The second study was an audit of Hospital Episode Statistics in England that spanned the introduction of smoke-free legislation in 2007.  They found a 4.9% (95% CI 0.6% to 9.0%) reduction in emergency hospital admissions for asthma.

NICE comments:

Both of these studies add to the growing evidence that smoke-free legislation is effective at reducing poor health.

As smoking is harmful, we can't do experiments to test the effectiveness of smoking bans.  This observational evidence is probably the best we will get.

As smoking is harmful, we can’t do experiments to test the effectiveness of smoking bans. This observational evidence is probably the best we will get.

Comments

  • As this is observational evidence, it is impossible to prove causation.  It could be that other factors, such as improvements in prenatal care, reduced the rate of preterm birth.  However, the consistency of the association is striking.
  • The researchers did adjust their analysis to take account of known confounders, such as changes in patterns of care, but they can’t take account of confounders they don’t know about.
  • There is an interesting Response to the preterm birth study on the BMJ website from Dutch researchers who did a similar analysis.  They report evidence of a reduction in preterm births since 2000, but no evidence of additional reductions when smoking bans were introduced.  This suggests there may indeed have been confounding from improvements in prenatal care.
  • In the case of asthma, similar studies in different settings have found similar results, suggesting that the picture is much clearer for smoking bans reducing asthma attacks by reducing passive smoking.

References

  1. National Institute for Health and Care Excellence (NICE).  Impact of smoke-free legislation on population health.  Eyes on Evidence 2014; 57.
  2. Cox, B., Martens, E., Nemery, B., Vangronsveld, J., Nawrot, T. Impact of a stepwise introduction of smoke-free legislation on the rate of preterm births: analysis of routinely collected birth data. BMJ 2013;346:f441.
  3. Sims M, Maxwell R, Gilmore A. Short-term impact of the smokefree legislation in England on emergency hospital admissions for asthma among adults: a population-based study. Thorax. 2013 Jul;68(7):619-24.