John: One of the most noticeable public health measures of recent years in several countries has been the ban on smoking in public places such as restaurants. A Cochrane Review is examining the health effects of these bans and it was updated in February 2016. We asked Kate Frazer from University College Dublin in Ireland, the first country in the world to introduce one of these national bans, to tell us about the expanding evidence base and the latest findings.

Kate: Tobacco is the second major cause of mortality and is responsible for one in ten adult deaths worldwide. Measures to control the demand for and supply of tobacco products and to protect public health have been advocated.  The World Health Organization has been pivotal in calling for smoke free environments.The WHO estimate that 600,000 people die each year from tobacco related diseases from the effects of second hand smoke.  Second hand smoke, also known as environmental tobacco smoke or passive smoke, is the combination of side stream smoke and mainstream smoke exhaled by a smoker. 
Second hand smoke is a complex mixture of gases and particulate matter emitted by the combustion of tobacco products.  It was declared carcinogenic by the International Agency for Research on Cancer. National smoke free legislation banning or restricting exposure to second hand smoke was first introduced in all indoor public places and workplaces in Ireland in 2004.  The primary outcome of legislation is to protect non smokers. Legislative smoking bans also offer the potential to influence social norms and the smoking behaviour of people who want to quit smoking.
The objectives of the Cochrane review were to assess the effects of a legislative smoking ban on morbidity and mortality from exposure to second hand smoke and to assess the effects of a legislative smoking ban on smoking prevalence and tobacco consumption. Since the previous version of the review had shown clear evidence that introducing legislation to ban smoking in public places does reduce exposure to econd hand smoke in those places, we did not include studies that only reported exposure to second hand smoke, studies had to include a measured health outcome.
There are 77 studies included in this updated review.  We retained 12 studies from the original and identified 65 new studies.  Evidence from 21 countries is provided, an increase in the number of countries from the first review.  There are no randomised controlled studies in this review due to a lack of feasibility in using this methodology in population level studies.  Smoking is a visible activity and countries cannot be randomised. 36 studies in the review used an interrupted time series design, 23 studies used a controlled before and after study design and 18 studies used a before and after study design with no control group. 44 studies in the review report cardiovascular health outcomes, 21 studies report respiratory health outcomes, 7 studies report perinatal health outcomes and 11 studies report national mortality rates for smoking related diseases. 24 studies evaluated the impact of legislative smoking bans on smoking behaviour.
There is consistent evidence in this review of a positive impact of a legislative smoking ban on reducing admissions for cardiovascular disease, specifically in 33 studies for acute coronary syndrome and for 5 of the 6 studies for stroke admissions.  The evidence identified reduced admissions for non smokers as well as smokers.
There was consistent evidence in 8 of the 11 studies of reduced mortality from smoking related diseases. The effects on respiratory health included reductions in admissions rates for asthma and chronic obstructive pulmonary disease. However the evidence was not consistent across all studies. More studies are required. Effects on perinatal health included reductions in low birth weights, reductions in maternal smoking rates and reductions in pre term births. However the evidence is not consistent across all 7 studies.  More studies are required. The effect of a legislative smoking ban on smoking prevalence and tobacco consumption rates is inconsistent, with some studies not detecting additional long term change in prevalence rates.
This updated review provides the clearest evidence yet and more robust support for the previous conclusions that the introduction of a legislative smoking ban does lead to improved health outcomes through a reduction in second hand smoke exposure for countries and their populations. 

John: Details of these health outcomes and the dozens of studies that are now included in Kate's review can be found in the full version, which is available online at Cochrane Library dot com. You can find it easily with a search for 'smoking bans'.