The law, banning smoking in cars carrying children, has seen the proportion of teens exposed to secondhand tobacco smoke fall by 72% in England, suggests an analysis of survey data, published online in the journal Thorax.
The legislation was introduced in England in October 2015 and in Scotland in December 2016, with the aim of cutting children's (under 18s) exposure to the harms of secondhand tobacco smoke, to which they are especially vulnerable.
The researchers drew on survey data for three years for both countries to assess the impact of the ban in England.
The data for England came from the Smoking, Drinking and Drug Use (SDDU) surveys for 2012, 2014, and 2016, while the information for Scotland came from the Scottish Health Survey.
Researchers focused on 13-15 year olds to avoid issues with parents reporting answers for younger children, potentially compromising the accuracy of the data. Children were asked how often, over the past year, they had travelled in a car with an adult who smoked during the journey.
Some 15,318 responses were received for teens in England, and 822 for their peers in Scotland.
The proportion of children exposed to secondhand tobacco smoke in Scotland fell from 3.4% in 2012 to 2.2% in 2014, and to 1.3% in 2016.
The equivalent figures for England were 6.3% and 5.9% before the ban took effect and 1.6% after it came into force, representing an absolute reduction of 4.1% and a fall of 72% when compared with the period before the ban.
Girls and those from areas of higher deprivation, as assessed by an amalgam of measures, were more likely to report secondhand tobacco smoke exposure in a car, prompting the researchers to highlight that this "serves as a reminder of the socially patterned risks of smoking."
This is an observational study, so can't establish cause, added to which, the data measured were not identical in both countries. But, say the researchers: "the design permits observed changes to be plausibly ascribed to the policy intervention."
And they conclude: "Our results suggest that banning smoking in private vehicles carrying children has been successful in its main aim of reducing their exposure to tobacco smoke.
"Given children's known vulnerability to secondhand smoke, reductions in exposure will probably result in improved health."
More information: Impact of banning smoking in cars with children on exposure to second-hand smoke: a natural experiment in England and Scotland, Thorax (2020). DOI: 10.1136/thoraxjnl-2019-213998
Journal information: Thorax
Provided by British Medical Journal