The popularity of e-cigarettes has soared in recent years, but do they pose a health risk we should be concerned about?
Many of the concerns arise from an apparent lack of evidence for the effects of e-cigarette use. As e-cigarette use is moving toward ubiquity, the gaps in knowledge about their effects are becoming more concerning for health experts.
Whether it is concerning how e-cigarettes are marketed or precisely what ingredients are contained within these devices, people are becoming wary of devices that originally appeared to be completely benign.
In a study of American adults published in Nicotine and Tobacco Research last year, 37% were opposed to e-cigarette use in smoke-free areas, with around 40% uncertain. This finding suggests both caution and uncertainty regarding the safety of e-cigarettes.
For this Spotlight feature, we take a look at what the apparent dangers associated with e-cigarette use are, aiming to assess just how worried, if at all, we should be about e-cigarettes.
E-cigarettes and their regulation
So what precisely are e-cigarettes comprised of that could make them dangerous? The majority of devices have a mouthpiece or cartridge, an atomizer and a battery. The cartridge holds a liquid solution (usually containing nicotine) that is heated up and vaporized by the atomizer. Once the liquid is vaporized, the user can inhale it, mimicking the process of smoking.
The solutions within the cartridges have variable concentrations of nicotine - amounts can range from no nicotine at all to high concentrations (24-36 mg/ml).
A report from the Centers for Disease Control and Prevention (CDC) published last year revealed that e-cigarette-related calls to poison centers in the US increased dramatically over the past 5 years. In 2010, there was one call per month, but this rose to around 215 calls per month by 2014.
Does this increase signal a dangerous toxicity in e-cigarettes? Dr. Tom Frieden, director of the CDC, stated that the report "raises another red flag about e-cigarettes: the liquid nicotine used in e-cigarettes can be hazardous."
Defenders of the device could point to how these poisonings occurred. More than half of the calls to poison centers involved children aged 5 years and under, suggesting that misuse of a product intended for adults was to blame.
E-cigarettes consist of cartridges, atomizers and power sources. There have been some concerns about health risks posed by the cartridges and the liquid solutions they contain.
According to the investigators, however, child poisoning was usually due to the direct contact with the cartridge liquid, either through ingestion, inhalation or exposure to the liquid on their skin or eyes.
"Use of these products is skyrocketing and these poisonings will continue," says Dr. Frieden. "E-cigarette liquids as currently sold are a threat to small children because they are not required to be childproof, and they come in candy and fruit flavors that are appealing to children."
The fact that e-cigarettes are not required to be childproof comes from their position in a regulatory gray area. At present, the US Food and Drug Administration (FDA) can only regulate e-cigarettes that manufacturers market as therapeutic, giving those who choose not to market their products this way more freedom to construct them as they please.
Last year, the FDA announced a proposal to extend current tobacco regulation to include all e-cigarettes and other products that meet the legal definition of a tobacco product. This would allow them to restrict the way e-cigarettes are advertised and promoted, especially campaigns designed to appeal to youths.
Until this proposed rule is finalized, the aspects of e-cigarette presentation that Dr. Frieden is most concerned about are likely to continue. Consumers will also have to wait for an accepted set of measures to confirm the purity of e-cigarettes and the liquids used within.
Substances in e-cigarettes
In terms of the chemicals contained in e-cigarettes, much is still unknown about precisely what is present and what their long-term effects are. While manufacturers will claim that their devices are safe, various studies have questioned this presumption.
The FDA themselves analyzed samples of two popular brands of e-cigarette. The investigators found variable levels of nicotine - perhaps not so much of a surprise - but also identified traces of toxic chemicals including carcinogens, substances known to cause cancer. Examples of these chemicals include formaldehyde and acetaldehyde.
After making these findings, the FDA issued a warning about the potential dangers of using e-cigarettes.
A study conducted by researchers from the University of Southern California found that the vapor produced by a popular brand of e-cigarette contained toxic levels of certain metals far greater than those found in the smoke of traditional cigarettes.
"Our results demonstrate that overall, electronic cigarettes seem to be less harmful than regular cigarettes, but their elevated content of toxic metals such as nickel and chromium do raise concerns," says Prof. Sioutas, coauthor of the study.
The researchers believe that these metal particles, mainly chromium and nickel, were likely to have come from the e-cigarette cartridges, suggesting that better manufacturing standards for the devices may be required.
Another study, published earlier this year in PLOS ONE, found that e-cigarette exposure could impair the antimicrobial defenses of the lungs in a mouse model.
This study has been criticized for only comparing the consequences of e-cigarette use with fresh air and not with smoking, as well as for using mice, known to be affected differently by nicotine than humans. However, the researchers state that their findings merely serve to illustrate a need for further testing before e-cigarettes can be portrayed as a safe alternative to traditional smoking.
Finally, researchers have also pointed out the dangers of nicotine, which is found in the majority of e-cigarettes. A study published last year in Oncotarget found that nicotine exposure caused cells to mutate in a manner similar to oxidative stress, a precursor to cancer.
The authors concluded that exposure to nicotine over a long period could lead to mutated genes that increase an individual's likelihood of developing cancer, even though nicotine itself is not yet considered to be carcinogenic.
Although e-cigarettes do not contain some of the most harmful substances found in traditional cigarettes - tobacco, tar and the chemicals produced by burning tobacco - and are, therefore, safer to use, there is evidence to suggest that e-cigarettes should not be viewed as being without risk.
Are e-cigarettes a smoking cessation aid or gateway to tobacco?
The main argument used in support of e-cigarettes - and consequently often their main selling point when it comes to marketing - is that they can help people quit smoking. This benefit means that even if there are some risks to their use, it is far more preferable that people use them compared with traditional cigarettes.
According to the National Institute on Drug Abuse (NIDA), however, it is unclear whether e-cigarettes may be effective as smoking-cessation aids.
In contrast, a Cochrane review - widely recognized as thorough and reliable forms of systematic review - published in December revealed that e-cigarettes can help smokers reduce or stop smoking. The findings of the review followed analysis of two randomized trials and 11 observational studies.
The authors of the review reported that their findings were encouraging, although the number of participants enrolled in each of the studies was limited.
Some public health experts believe that rising levels of e-cigarette use among adolescents could lead to more taking up traditional cigarettes.
The Cochrane review may assuage concerns about the efficacy of e-cigarettes, but some public health experts are also concerned that use of the devices could work the other way as well, acting as a "gateway" or an introductory product for people - particularly youths - to try traditional cigarettes.
This particular fear has grown due to the increase in marketing that may appeal to adolescents. A study published last year revealed that exposure to e-cigarette advertising on television to young adults (ages 18-24) rose by 321% between 2011 and 2013.
At the same time, the CDC reported that e-cigarette use had more than doubled among middle and high school students in the US from 2011-12, with more than 1.78 million middle and high school students having used the devices in 2012. While some states have prohibited the sale of e-cigarettes to minors, the devices are easily acquired via the Internet.
"The increased use of e-cigarettes by teens is deeply troubling," states Dr. Frieden. "Nicotine is a highly addictive drug. Many teens who start with e-cigarettes may be condemned to struggling with a lifelong addiction to nicotine and conventional cigarettes."
However, many people dispute the idea that e-cigarettes can lead to traditional cigarettes, including some antismoking groups.
"Electronic cigarettes have been shown to help people quit smoking and there is no evidence to currently suggest that they act as a gateway to smoking for young people in the UK," state Action on Smoking and Health (ASH), a UK charity set up to eliminate the harm caused by tobacco.
"Research suggests that smoking rates amongst UK children overall, while still too high, have continued to decline since the emergence of e-cigarettes last decade," reports Dr. Penny Woods, Chief Executive for the British Lung Foundation, implying that e-cigarettes may be contributing to falling smoking rates.
The Mayo Clinic suggest that until more is known about these potential risks, there are many other FDA-approved medications that are proven to be both safe and effective in helping people to quit smoking.
An interesting piece of trivia that may or may not be pertinent is that the inventor of e-cigarettes, a pharmacist from China called Hon Lik, had hoped to quit smoking but now uses both e-cigarettes and traditional cigarettes. He states that he only smokes tobacco in order to check the flavors in his devices, however.
Lack of evidence on e-cigarettes
One thing that is clear from looking at what has been written so far about e-cigarettes is that a lack of robust evidence is both driving debate about their use and hindering the arguments put forward by both sides.
Policy makers who are restricting the use of e-cigarettes in public places are being criticized due to strong evidence finding that the devices are dangerous. Manufacturers promoting e-cigarettes as smoking cessation devices are in turn criticized for a lack of strong evidence proving their efficacy.
In this investigation, it appears that e-cigarettes are safer than traditional cigarettes but may have their own risks that are worth considering.
Dr. Nick Hopkinson, an honorary medical advisor to the British Lung Foundation, suggests that as e-cigarettes are certainly far less harmful than normal cigarettes, completely replacing tobacco with the electronic devices should improve health. However, avoiding both electronic and traditional cigarettes is preferable.
"Although safer than smoking, the long-term health impact of e-cigarettes is still not fully known and in need of further research," he adds. "We would recommend that anyone using e-cigarettes to quit smoking, especially if they have lung disease, should eventually try to quit using [e-cigarettes] too."