Using e-cigarettes raises the risk of heart attacks by a third, researchers have warned.
Concerns are growing around the world about the long-term health impact of vaping, amidst booming popularity of the devices.
Yet e-cigarettes remain at the heart of public health policy, with officials repeatedly insisting the benefits far outweigh any potential harms.
The study, to be presented at the American College of Cardiology conference in New Orleans later this month, is one of the largest ever conducted on the impact of vaping.
Scientists found vaping boosts the risk of a heart attack and a stroke by 56 per cent and 30 per cent, respectively
Experts from the University of Kansas examined data from more than 90,000 e-cigarette users.
They found people who vaped every day were 34 per cent more likely than non-e-cigarette users to suffer a heart attack, and those who used the devices more sporadically had a 29 per cent increased risk.
Study leader Dr Mohinder Vindhyal said: 'Until now, little has been known about cardiovascular events relative to e-cigarette use.
'These data are a real wake-up call and should prompt more action and awareness about the dangers of e-cigarettes.'
He admitted the study was not perfect – most of the e-cigarette users were ex-smokers so the heart problems could be due to their lifetime of tobacco use.
But he stressed that his team had tried as far as possible to take smoking into account, adding: 'I wouldn't want any of my patients nor my family members to vape.'
Roughly a third of the 90,000 e-cigarette users were also smokers.
The team's initial analysis suggested e-cigarette users had a 56 per cent increased risk of heart attack than those who did not vape.
But taking into account the fact that people who were also regularly smoking tobacco had a 165 per cent increased heart attack risk, they calculated the increased isk of vaping alone dropped to about 34 per cent.
They found e-cigarette users were also 55 per cent more likely to suffer from depression or anxiety.
Dr Vindhyal, however, admitted his team could not completely eradicate the impact of previous tobacco use, because virtually all e-cigarette users in the study had smoked tobacco in the past.
The flavourings in electronic cigarettes may damage blood vessels in the same way as heart disease, according to research published in June.
The chemicals used to give the vapour flavours, such as cinnamon, strawberry and banana, can cause inflammation in cells in the arteries, veins and heart.
They causes the body to react in a way that mimics the early signs of heart disease, heart attacks or strokes, the study by Boston University found.
Other recent studies have also suggested smoking e-cigarettes could cause DNA mutations which lead to cancer, and enable pneumonia-causing bacteria to stick to the lungs easier.
Researchers at New York University subjected human bladder and lung cells to e-cigarette vapor, which is marketed as being healthier than tobacco.
They found the cells mutated and became cancerous much faster than expected and mice exposed to the vapour also suffered significant DNA damage.
In another study, scientists at Queen Mary University, London, found vaping makes users more likely to catch pneumonia – just like smoking tobacco or breathing in traffic fumes.
The vapour from e-cigarettes helps bacteria which cause the condition to stick to the cells that line the airways, they said.
The effect occurs with traditional cigarette smoke and those who are exposed to air pollution high in particulates from vehicle exhausts.
