Use of e-cigarettes may significantly increase a person's risk of developing chronic lung diseases like asthma, bronchitis, and emphysema, according to a study published on Monday.
Researchers from the University of California, San Francisco in the US also found that people who used e-cigarettes and smoked tobacco -- the most common pattern among adult e-cigarette users -- were at an even higher risk of developing chronic lung disease than those who used either product alone.
The findings, published in the American Journal of Preventive Medicine, are based on an analysis of publicly available data from the Population Assessment of Tobacco and Health (PATH), which tracked e-cigarette and tobacco habits as well as new lung disease diagnoses in over 32,000 American adults from 2013 to 2016.
Several earlier population studies had found an association between e-cigarette use and lung disease at a single point in time.
However, these studies provided a snapshot that made it impossible for researchers to say whether lung disease was being caused by e-cigarettes or if people with lung disease were more likely to use e-cigarettes.
The researchers started with people who did not have any reported lung disease, taking account of their e-cigarette use and smoking from the start.
They then followed them for three years, offering stronger evidence of a causal link between adult e-cigarette use and lung diseases than prior studies.
"What we found is that for e-cigarette users, the odds of developing lung disease increased by about a third, even after controlling for their tobacco use and their clinical and demographic information," said Stanton Glantz, a professor at the University of California, San Francisco.
"We concluded that e-cigarettes are harmful on their own, and the effects are independent of smoking conventional tobacco," Glantz said in a statement.
Though current and former e-cigarette users were 1.3 times more likely to develop chronic lung disease, tobacco smokers increased their risk by a factor of 2.6, the researchers said.
For dual users -- people who smoke and use e-cigarettes at the same time -- these two risks multiply, more than tripling the risk of developing lung disease, they said.
"Dual users -- the most common use pattern among people who use e-cigarettes -- get the combined risk of e-cigarettes and conventional cigarettes, so they're actually worse off than tobacco smokers," said Glantz.
This finding is particularly relevant as the debate continues to rage over whether e-cigarettes should be promoted as a harm-reduction tool for smokers, the researchers said.
While they found that switching from smoked tobacco to e-cigarettes lowered the risk of developing lung disease, fewer than one per cent of the smokers had completely switched to e-cigarettes.
