"Laws banning smoking in public places have had a positive impact on child health," BBC News reports. Researchers found lower rates of preterm births and childhood severe asthma cases after the introduction of smoke-free laws.
11 studies published between 2008 and 2013 were reviewed, in a bid to examine the effect smoking bans around the world have had on child health. In particular, the effects on preterm birth, low birth weight and childhood hospital attendances for asthma were noted.
They found there was a 10% drop in preterm births and childhood asthma after the introduction of smoking bans, but that smoking bans had not had a significant effect on low birth weight.
These results are biologically plausible. However, all 11 studies only looked at changes in the rates of childhood health outcomes before and after smoking bans were introduced, meaning that it is difficult to pinpoint smoking bans as the single, direct cause of any differences. Numerous other changes could have been responsible for the differences seen.
Despite this limitation, this research provides further support for smoke-free environments.
As well as the risks mentioned above, smoking around children can increase their risk of coughs and colds, ear infections and even fatal conditions, such as meningitis and cot death. Read more about the dangers of exposing children to passive smoking.
If you are a smoker who lives in a home with children, you should try to stop smoking, or at least do it in an outside area, away from sight.
Where did the story come from?
The study was carried out by researchers from Maastricht University (Netherlands); The University of Edinburgh (UK); Hasselt University and the University of Leuven (Belgium); and Brigham and Women’s Hospital/Harvard Medical School (US).
It was funded by the Thrasher Fund, Lung Foundation Netherlands, International Paediatric Research Foundation, Maastricht University and the Commonwealth Fund, which is a private philanthropic institute.
The study was published in the peer-reviewed medical journal The Lancet.
The results of the study were well reported by BBC News and The Guardian.
What kind of research was this?
This was a systematic review and meta-analysis of studies that had examined the effect of smoke-free legislation on children’s health.
A systematic review is an overview of primary studies. They use explicit and reproducible methods to search for and assess studies for inclusion in the review.
A meta-analysis is a mathematical synthesis of the results of the included studies, and is an appropriate way of pooling and studying the body of available evidence on a specific topic.
The researchers performed this study to help inform national and international policy decision on the implementation of smoke-free legislation.
Most developed countries now have some type of smoke-free legislation.
What did the research involve?
The researchers searched databases of published literature and the WHO International Clinical Trials Registry Platform. They also consulted with an expert panel to identify:
- randomised controlled trials
- controlled clinical trials
- controlled before and after studies
- a interrupted time series (see below) that reported links between smoking bans in workplaces and/or public places, and health outcomes in children
Once the studies had been identified, the researchers assessed the quality of the studies, to see if there were any biases, and extracted data about their characteristics and results.
The researchers then performed a meta-analysis to combine the results of the included studies.
What were the basic results?
The researchers identified 11 studies, which were all interrupted time series. In this type of study, information is collected at multiple time points before and after an intervention – in this case, the introduction of a smoking ban. Interrupted time series aim to determine if the intervention has an effect significantly greater than the underlying trend. For example, a particular health outcome might have been falling before the intervention. If a before-and-after study had been performed, it might have incorrectly concluded that the intervention had an effect. By taking observations at multiple time points before and after the intervention, this trend would have been seen in an interrupted time series.
After the results of the studies were pooled in a meta-analysis, smoke free legislation was associated with:
- a 10% reduction in the relative risk of preterm birth (-10.4%, 95% Confidence Interval [CI] -18.8 to -2.0). This was based on the results of four studies, with a total of 1,366,862 people.
- a 10% reduction in the relative risk of hospital attendances for asthma (-10.1%, 95% CI -15.2 to -5.0). This was based on the results of three studies, with a total of 225,753 people.
- no change in the relative risk of low birth weight (-1.7%, 95% CI -5.1 to 1.6). This was based on the results of six studies, with more than 1.9 million people.
How did the researchers interpret the results?
The researchers concluded that “smoke-free legislation is associated with substantial reductions in preterm births and hospital attendance for asthma. Together with the health benefits in adults, this study provides strong support for WHO recommendations to create smoke-free environments”.
This systematic review and meta-analysis found there was a 10% drop in preterm births and childhood asthma after the introduction of a smoking ban. However, smoking bans were found not to have a significant effect on low birth weight.
These results are biologically plausible. Previous research suggests that exposure to smoke in pregnancy may have a negative impact on pregnancy outcomes. Similarly, exposure to smoke in early childhood may increase the risk of a child of developing a respiratory condition such as asthma.
However, as all of the studies only examined changes in the rates of childhood health outcomes before and after smoking bans were introduced, it is difficult to pinpoint smoking bans as the single direct cause of any differences. Numerous other changes could have been responsible for the differences seen.
If smoking bans have had a direct influence on the changes seen, it is difficult to know why this is the case. For example, both preterm birth and childhood asthma are known to be associated with smoking; it is possible that the decline in the rates of both since the introduction of a smoking ban could be the result of pregnant women or children having less secondhand smoke exposure in public places.
However, it could also be due to increased public awareness of the detrimental health effects of smoking around the time of ban, which could have influenced smokers’ behaviour. For example, pregnant women may have been more likely to give up smoking themselves, or make sure that they were not exposed to smoke.
Similarly, parents/carers who smoked could have become more aware of the effects it could have on their child(ren). As a result, they could consciously make sure not to smoke in the house or car when children were present.
Overall, although time trend studies can suggest that a particular factor is associated with particular outcomes, it is difficult to know exactly how or why this change has occurred.
All of the included studies were carried out in Europe or North America – this means that the results cannot necessarily be extrapolated and generalised on a global scale.
Despite these limitations, this study does provide further support for smoke-free environments and the importance of not exposing children to passive smoking.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
The Guardian, 28 March 2014
BBC News, 28 March 2014
Links to the science
The Lancet. Published online March 28 2014