Young Britons see significantly more on-screen smoking in movies than their US peers, finds research published ahead of print in the journal Tobacco Control.
The UK film classification system, which rates more films as suitable for young people than its US counterpart, is to blame, say the authors.
The research team assessed the number of on-screen smoking/tobacco occurrences in 572 top grossing films in the UK, which included 546 screened in the US plus 26 high earning films released only in the UK.
They then divided the total box office earnings of each film by the year's average ticket price, to calculate the estimated number of 'tobacco impressions' delivered to cinema going audiences for each film.
A 'tobacco impression' is defined as one person seeing an occurrence of smoking or tobacco on one occasion, with the cumulative number of impressions a measure of how much the film encourages smoking.
Among the 572 films assessed, more than two thirds (69%) featured tobacco. Of these, more than nine out of 10 were classified as suitable for adolescents ('15' or '12A') under the UK ratings system.
In all, 5.07 billion tobacco impressions were delivered to UK cinema going audiences during the period under study, of which 4.49 billion (89%) were delivered in '15' and '12A' rated films.
Because 79% of the films rated only for adults in the US ('R') were classified as suitable for young people in the UK, this meant that young Britons were exposed to 28% more smoking impressions in '15' or '12A' rated movies than their US peers, calculate the authors.
Although UK produced films contained more instances of smoking, on average, than US produced films, the market dominance of the latter meant that Hollywood was responsible for most of the tobacco impressions delivered to UK audiences in 2001-6, say the authors.
Evidence from several countries, including the US, suggests that the more smoking young people are exposed to in movies, the more likely they are to start smoking themselves. Those who see the most are around three times more likely to take it up than those who see the least, say the authors.
Awarding an '18' rating to films that contain smoking "would create an economic incentive for motion picture producers to simply leave smoking out of films developed for the youth market," say the authors.
When they compared total box office sales of a random sample of 40 films rated suitable for children and 40 rated '18', they calculated that films targeted at young people grossed 1.75 times as much as those targeting adult audiences.
"The decision to classify a film as appropriate for youths clearly has economic benefits for the film industry," they say.
And they conclude: "A film classification policy that keeps on-screen smoking out of films rated suitable for youths ... would reduce this exposure for people under 18 years of age and probably lead to a substantial reduction in youth smoking."