Researchers from the University of Cambridge and the University of North Carolina recruited more than 400 English children for the study.
The children were aged 11 to 16, had never smoked or vaped before, and were randomly allocated to one of three groups.
One group was shown 10 advertisements depicting e-cigarettes as glamorous, a second group was shown 10 adverts that portrayed them as healthy, and a third control group was shown no adverts.
The children were then asked a series of questions aimed at determining their attitudes towards smoking and vaping.
Children shown the adverts were no more or less likely than the control group to perceive tobacco smoking as appealing, and all three groups understood that smoking more than 10 cigarettes a day was harmful.
However, both groups exposed to the e-cigarette adverts were less likely to believe that smoking one or two tobacco cigarettes occasionally was harmful.There is concern that the increasing exposure of children to e-cigarette adverts could be contributing to high rates of experimentation.
In the US, adolescents’ exposure to e-cigarette adverts on TV more than trebled between 2011 and 2013, researchers said.
They added that estimates suggest that, among children who try smoking, between a third and a half of them are likely to become regular smokers within two to three years.
Dr Milica Vasiljevic, from the Department of Public Health and Primary Care at the University of Cambridge, said: “While we can be optimistic that the adverts don’t seem to make tobacco smoking more appealing to young people, they do appear to make occasional smoking seem less harmful.
“This is worrying, as we know that even occasional tobacco smoking is bad for your health, and young people who smoke occasionally believe they are somehow immune to its effects and do not feel the need to quit.”
The group shown ads depicting e-cigarettes as glamorous also believed e-cigarette vaping to be more prevalent than did the other two groups.
Researchers also highlighted a 2014 study that showed more children aged 11 to 15 experimented with e-cigarettes than tobacco (22% compared with 18%).
Professor Theresa Marteau, director of the Behaviour and Health Research Unit and a Fellow of Christ’s College at University of Cambridge, said: “E-cigarette marketing across Europe is regulated under the new EU Tobacco Products Directive, which came into effect on May 20 this year.
“The directive limits the exposure of children to TV and newspaper e-cigarette adverts. However, it does not cover advertising in the form of posters, leaflets, and adverts at point of sale, nor does it cover the content of marketing materials depicting e-cigarettes as glamorous or healthy.
"The findings from our study suggest these omissions could present a threat to the health of children.”
The research was published in the journal Tobacco Control.