Researchers suggest e-cigarette vapor causes cancer-related cell damage.
Co-lead study author Dr. Jessica Wang-Rodriquez, professor of pathology at the University of California-San Diego, and colleagues publish their findings in the journal Oral Oncology.
Use of e-cigarettes (electronic cigarettes) has become popular in the US; a recent study from the Centers for Disease Control and Prevention (CDC) found that almost 13% of Americans have tried e-cigarettes at least once in their lifetime, with more than a fifth of adults aged 18-24 having used the devices.
While e-cigarettes do not contain tobacco - like conventional cigarettes - the vapor produced by the device and inhaled by users does contain nicotine flavorings and other chemicals. Nicotine is the chemical that makes smoking addictive.
How such chemicals impact human health has been a hot topic in recent years; while some studies have suggested e-cigarettes are significantly less harmful than standard cigarettes and can successfully help smokers quit, others have suggested the devices are harmful to health.
A recent study by Harvard researchers, for example, found that many flavored e-cigarette liquids contain chemicals that are associated with "popcorn lung" - a severe respiratory condition characterized by scarring of the lung's tiny air sacs.
Now, Dr. Wang-Rodriquez and colleagues have found that e-cigarettes may cause significant damage to human cells that may lead to cancer.
Even nicotine-free e-cigarette vapor caused cell damage
To reach their findings, the team applied extracts of vapor from two popular e-cigarette brands to healthy human epithelial cells - cells that line organs, glands and cavities throughout the body - in a petri dish, comparing the effects with untreated cells. One vapor tested contained nicotine and the other did not.
Fast facts about e-cigarette use in the US
- A 2014 CDC report found that men were more likely than women to have ever tried an e-cigarette
- Rates of current e-cigarette use are similar between men and women
- Around 1 in 6 current cigarette smokers also use e-cigarettes.
"There haven't been many good lab studies on the effects of these products on actual human cells," notes Dr. Wang-Rodriquez.
The researchers found that cells exposed to the e-cigarette vapor extracts were more likely to suffer DNA damage and death than non-exposed cells.
In detail, the exposed cells showed breaks in DNA strands - a process that can lead to cancer. Additionally, exposed cells were more likely to enter apoptosis and necrosis; both are forms of cell death, with the latter triggered by external factors, such as a bodily injury or poison.
Interestingly, the researchers found these effects still occurred with the vapor extract that was free of nicotine, albeit at lower levels, suggesting there are chemicals other than nicotine present in e-cigarettes that can cause cell damage.
"There have been many studies showing that nicotine can damage cells," says Dr. Wang-Rodriquez. "But we found that other variables can do damage as well. It's not that the nicotine is completely innocent in the mix, but it looks like the amount of nicotine that the cells are exposed to by e-cigarettes is not sufficient by itself to cause these changes."
"There must be other components in the e-cigarettes that are doing this damage," she continues. "So we may be identifying other carcinogenic components that are previously undescribed."
E-cigarettes 'no better than smoking regular cigarettes'
The team admits that there are some limitations to their study. For example, they point out that the human cell lines used in the research are not fully comparable to cells present in a living individual, so it is possible that e-cigarette vapors may have different effects in the human body.
Additionally, the researchers did not simulate the vapor dose to which e-cigarette users would normally be exposed. "In this particular study, it was similar to someone smoking continuously for hours on end, so it's a higher amount than would normally be delivered," notes Dr. Wang-Rodriquez.
She adds that the team plans to conduct further research to determine what dose of e-cigarette vapor is likely to cause DNA damage.
While the question of whether e-cigarettes are healthier than conventional cigarettes remains unanswered, Dr. Wang-Rodriquez believes the electronic devices are just as harmful:
"Based on the evidence to date, I believe they are no better than smoking regular cigarettes."
Aside from the negative health implications associated with e-cigarette use, concerns have been raised that the devices may act as a gateway to conventional smoking. A recent study reported by Medical News Today, for example, found that almost 70% of participants took up regular smoking within 1 year of initiating e-cigarette use.