Vaping is just as bad as cigarettes for your heart, a landmark health study funded by the US Government has found.
Experts have found two studies, in mice and on people, similar damage was caused to blood vessels using e-cigarettes as smoking tobacco.
Damage to blood vessels or those which are not functioning properly make it more difficult for oxygen-blood to reach the heart and other parts of the body.
A combination of smoking and vaping may result in more damage for those using vaping devices to help them quit.
Tobacco, however, is still thought to be worse for health than e-cigarettes because of its connection lung cancer and breathing issues.
The study shows vapes are not the risk-free alternative to cigarettes.
It comes after federal data showed more than 2.55 million middle or high school pupils had used an e-cigarettes in the last 30 days.
Among US adults almost 10% vaped, data shows from the Centers for Disease Control and Prevention.
And regulators say the situation is as a 'vaping epidemic'.
Long-term use of either product damaged blood vessels, but each caused adverse effects the other did not.
This suggested using both products made the damage worse.
Researchers in the study were funded by the National Heart, Lung, and Blood Institute, part of the National Institutes of Health.
Research by experts from the University of California, San Francisco was published in the American Heart Association’s journal Arteriosclerosis, Thrombosis and Vascular Biology (ATVB).
Both types of smoking are known to impair endothelial function which causes large blood vessels to provide sufficient blood to the heart and other tissues.
The findings were discovered using mice and humans in two separate studies.
Using mice, researchers tried to discover if components of tobacco smoke or e-cigarette vapor were responsible for damage to blood vessels.
They measured ability of the blood vessels to widen, after exposure to smoke from four kinds of cigarettes:
Blood vessel shrinkage was reduced in all four types of cigarettes.
Rats were also exposed to two gases found in smoke and e-cigarette aerosol, plus clean carbon particles to measure their effects on blood vessel shrinkage.
Researchers found damage did not appear be caused by a particular component of cigarette smoke or e‑cigarette vapor.
It was instead caused by airway irritation which affected involuntary internal organ functions, that leads to blood vessel damage.
Dr Matthew L. Springer, professor of medicine at the University of California, said: "We were surprised to find that there was not a single component that you could remove to stop the damaging effect of smoke or vapors on the blood vessels.'
"As long as there’s an irritant in the airway, blood vessel function may be impaired."
In the study researchers recruited 120 volunteers including long-term e-cigarette users, long-term cigarette smokers, and non smokers.
Blood sample were collected and those from the e-cigarette users and smokers had a significantly greater decrease in nitric oxide production than the blood of nonusers.
E-cigarette users had more permeability in the blood vessel cells than those of both tobacco smokers and nonusers.
Scientists concluded blood from tobacco smokers had higher levels of cardiovascular risks and e-cig users' blood had raised levels of of cardiovascular risks.
Dr Springer said: "These findings suggest that using the two products together, as many people do, could increase their health risks compared to using them individually... We had not expected to see that."
The results suggested regulators including Food and Drug Administration cannot rely on banning certain ingredients to avoid adverse health effects.
'Dr Springer added: "Smoking and vaping can have similar harmful cardiovascular effects but each condition causes some potentially harmful effects that the other does not.
"These differences indicate that dual product use, meaning smoking combustible cigarettes and also using e-cigarette products, may actually be worse for vascular health than either smoking or vaping alone."
