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London: Using e-cigarettes is no safer than smoking tobacco with nicotine, scientists warned after finding the vapour damages DNA and could cause cancer.
Researchers at the University of California created an extract from the "smoke" of e-cigarettes and used it to treat human cells in a laboratory.
The exposed cells developed DNA damage and died far sooner than untreated ones. Nicotine-free e-cigarettes caused 50 per cent more DNA strand breaks; for those with nicotine, the damage rose three-fold in eight weeks.
Dr Jessica Wang-Rodriguez, professor of pathology at the university in San Diego, said: "Our study strongly suggests that electronic cigarettes are not as safe as their marketing makes them appear. E-cigarettes on the whole have something to do with increased cell death. We hope to identify the individual components that are contributing.
"Based on the evidence to date I believe they are no better than smoking."
She plans further studies to see if the effects remain at lower doses.
Scientists and health officials are divided over e-cigarettes: Public Health England (PHE) said "vaping" is far safer but the World Health Organisation remains concerned. The study used normal epithelial cells, which line organs, glands and cavities such as the lungs.
Ones exposed to the vapour showed forms of damage, including DNA strand breaks. The double helix that makes up DNA has two molecule strands. When one or both break and cell repair does not work it raises the risk of cancer.
The team tested two types of each e-cigarette: nicotine ones caused most damage but vapour from nicotine-free versions was still enough to alter cells.
Scientists know of some troubling chemicals in the products such as formaldehyde, a carcinogen. Another possible culprit is diacetyl, a flavouring agent linked to lung disease. There are nearly 500 brands of e-cigarettes, in more than 7000 flavours, on sale.
PHE says it is important to provide smokers with tools to help them quit. Professor Kevin Fenton, its national director of health and wellbeing, said its recent review found e-cigarettes carry a fraction of the risk of smoking:
"The harmful chemicals found in tobacco smoke ... are either absent in e-cigarette vapour or, if present, are mostly at levels one-hundredth to one-thousandth found in tobacco smoke."
The research was published in the Journal of Oncology.