The study, accepted by the journal Addiction and published online Tuesday, comes as U.S. regulators weigh new rules for nicotine vaporizers. The e-cig industry and public health officials are battling over whether the devices should be treated as less-harmful cigarettes that help smokers give up tobacco or as a gateway that will lead adolescents to a deadly habit. Investigators from a cancer research center at the University College London conducted the study, which was partially funded with government and drug industry grants. None of the authors reported financial ties to e-cigarette companies, which adds to the report’s credibility.