Vaping is more harmful than first thought, study finds
But more long-term studies are needed.
Vaping can damage vital immune system cells and could be more harmful than initially thought, according to a study from the University of Birmingham.
The study, published in the British Medical Journal, suggested that vaping speeds up the death of lung cells by 50 fold and could trigger lung diseases in later life.
Researchers in the study warned vapers "against the widely held opinion that e-cigarettes are safe".
The small experimental study, led by Prof David Thickett, at the University of Birmingham, is available online in the journal Thorax.
Researchers mimicked vaping in a laboratory, testing the effect of e-cigarette vapour condensate on alveolar macrophages extracted from the lung tissue samples of eight non-smokers.
It found that the vapour caused inflammation and impaired the activity of alveolar macrophages cells, which remove dust particles, bacteria and allergens.
However, the study was led by Prof David Thickett, who said that the results don't show that e-cigarettes are more harmful than ordinary cigarettes, but urged caution over claims they are entirely safe.
He also advised that further research is required to fully understand the long-term health impact of vaping.
"In terms of cancer causing molecules in cigarette smoke, as opposed to cigarette vapour, there are certainly reduced numbers of carcinogens," he said.
"They are safer in terms of cancer risk - but if you vape for 20 or 30 years and this can cause COPD [chronic obstructive pulmonary disease], then that's something we need to know about.
"I don't believe e-cigarettes are more harmful than ordinary cigarettes - but we should have a cautious scepticism that they are as safe as we are being led to believe," Prof Thickett said.
The results of this study are at odds with an independent review conducted by Public Health England earlier this year which said that e-cigarettes are at least 95% less harmful than smoking.
The HSE discusses e-cigarettes on its website, and states: "We don't really know until they have been thoroughly assessed and monitored in a large population over time.
"E-Cigarettes contain nicotine which is addictive. E-cigarette vapour also contains propylene glycol, which has not been adequately studied with regard to its safety when heated and inhaled deeply and repeatedly. Also present are a variety of additives and contaminants."