London - E-cigarettes promoted as a way to quit smoking could pose a serious heart risk, a study warns.
A panel of experts assessed all available evidence about the safety of electronic cigarettes and said using them was not worth the danger.
They said: "E-cigarettes are not a harm-free alternative to tobacco smoke. Great caution and hesitation should remain concerning e-cigarette use until its health risk profile is better established."
Metals, particles and flavourings in the devices can increase blood pressure, heart rate and inflammation, and can stiffen the arteries, each of which raises the risk of heart disease, they said.
The conclusions by experts from Ohio State University reveal the gulf in the attitude towards e-cigarettes between the medical establishment in the US and that in the UK, where most experts see them as useful health tools.
British officials insist e-cigarettes should be pushed as a successful alternative to tobacco.
But US experts are alarmed by the accelerating popularity of vaping by teenagers and reports of deaths linked to e-cigarettes.
The American review was commissioned and published by Cardiovascular Research, the journal of the European Society of Cardiology, of which most British heart specialists are members.
Review researcher Professor Loren Wold said: "Many people think these products are safe, but there is more and more reason to worry about their effects on heart health.
"We know problems are seen in studies looking at the short-term effects of vaping, but that research is inconsistent and the impact of chronic e-cigarette use is an outright mystery. The potential harm to the heart over time is essentially unstudied."
E-cigarettes contain a liquid form of nicotine that is heated into vapour to be inhaled, avoiding the harm caused by tobacco smoke.
But critics say many adults and children use the devices as a lifestyle or fashion accessory, and some have never touched tobacco.
Nicholas Buchanan, the study’s lead author, said: "Especially for someone who has never smoked, it is just not worth the risk and it seems pretty conclusive that you can say they’re not harm-free. Most concerning are the numbers of children picking up the habit. We have no idea what the health implications are for them down the road."
However, Professor John Newton, director of health improvement at Public Health England, said: "PHE has always been clear that vaping is not without risks. If you don’t smoke don’t vape. But if you smoke there is no situation where it would be better for your health to continue smoking rather than switching to vaping."