A study in mice has found that e-cigarettes disrupt lung function and increase the risk of infection.
The findings, published in the Journal of Clinical Investigation, found that chronic exposure to nicotine-free vapours from e-cigarettes disrupts normal lung function and the ability of immune cells to respond to viral infection in mice.
Thus far, other studies have shown mixed results on the effects of vaping on health which led to the researchers doing their own investigations.
E-cigarettes are particularly popular in young people, especially in the US, according to co-author Dr Farrah Kheradmand, a lung expert and professor of medicine at Baylor College of Medicine. "E-cigarettes currently are the most commonly consumed tobacco substitute in the adolescent population. More than 3 million high school age adolescents as well as about 10 million adults in the US are active users."
In the study, one group of mice was exposed to e-cigarette smoke containing nicotine, another to e-cigarette smoke without nicotine. Another two groups were exposed to tobacco smoke or clean air. The mice were exposed to tobacco smoke or e-cigarette vapours for four months following a routine similar to a human smoking from their teenage years to their fifties.
As expected, the mice exposed to cigarette smoke had severely damaged lungs and inflammation resembling emphysema in human smokers. Surprisingly, damage was also found in the mice exposed to e-cigarette smoke not containing nicotine, which is currently considered to be safe. Researchers observed an unusual build-up of fats in the lungs which disrupted normal lung structure and function.
The build-up of fat was not from the solvent ingredients in the e-cigarette vapour but from the abnormal turnover of the protective fluid layer in the lungs. A build-up of fats was also seen in immune cells in the lungs. When the mice were exposed to the flu virus, these cells responded poorly to the infection.
"In summary, our experimental findings reveal that, independent of nicotine, chronic inhalation of e-cigarette vapours disrupts normal murine lung function and reduces the ability of resident immune cells to respond to infection, increasing the susceptibility to diseases such as influenza," said Dr Kheradmand. "Our experimental findings share similarities with previous multiple case reports describing the presence of lipid-laden macrophages in pulmonary fluid from people with e-cigarette-associated pneumonia. Our results support further investigations into the solvents used in vaping."
There are at least 2.5 million e-cigarette users in the UK. Public Health England maintains its position that e-cigarettes, whilst not risk-free, are at least 95% less harmful than cigarettes. In the UK, vaping is largely confined to current or ex-smokers who have quit using an e-cigarette. Many stop-smoking services use e-cigarettes as part of their smoking cessation programme.
Professor John Britton, director of the UK Centre for Tobacco and Alcohol Studies, University of Nottingham, who was not involved with the research, pointed out the limitations of studying animals, rather than humans.
"This will be helpful to doctors who are consulted by mice thinking of moving into a cage full of smoke or vapour for the rest of their lives," he said. "Lungs are delicate organs, and long-term inhalation of anything other than clean air is likely to cause damage, but the relevance of damage to mouse lungs to human health is far from clear."
This study was published in the Journal of Clinical Investigation.