The debate over the safety of e-cigarettes has taken another turn after US researchers found evidence to suggest that they are toxic to human airway cells, suppress immune defences and alter inflammation, while also boosting bacterial virulence.

Researchers at the University of California, San Diego School of Medicine and Veterans Affairs San Diego Healthcare System said inflammatory markers in the airways and blood of mice that inhaled e-cigarette vapours for one hour a day, five days a week, for four weeks were elevated by 10 percent compared to unexposed mice.

Conversely, their research, published in the Journal of Molecular Medicine, showed that bacterial pathogens seemed to benefit from exposure to e-cig vapour. Staphylococcus aureus bacteria were better able to form biofilms, adhere to and invade airway cells and resist human antimicrobial peptides after exposure to e-cigarette vapour, the team said.

Moreover, bacteria exposed to ‘vapour’ were also found to be more virulent in a mouse model of pneumonia; all mice infected with normal methicillin-resistant S. aureus survived, while 25 percent of those infected with MRSA pre-exposed to e-cigarette vapour died.

'Disease causing'

“We don't know specifically which lung and systemic diseases will be caused by the inflammatory changes induced by e-cigarette vapor inhalation, but based on clinical reports of acute toxicities and what we have found in the lab, we believe that they will cause disease in the end,” said senior author Laura E. Crotty Alexander, staff physician at the Veterans Affairs San Diego Healthcare System and assistant clinical professor at UC San Diego School of Medicine, commenting on the findings.

“Some of the changes we have found in mice are also found in the airways and blood of conventional cigarette smokers, while others are found in humans with cancer or inflammatory lung diseases.”

UK regulators recently issued the first licence for an electronic cigarette, thereby classing it a medicine and paving the way for its prescription on the National Health Service, despite big question marks over their long-term safety and regulation.

While Public Health England reported findings of an independent review concluding that e-cigarettes are 95% safer than smoking tobacco, research by the University of California, published in Oral Oncology, concluded that vaping is no safer than smoking as the process can still damage DNA and lead to cancer.