A recent outbreak of deadly lung illnesses linked to vaping has put the practice in health professionals and regulators crosshairs. Now the first longitudinal population-based study of e-cigarette use in a representative sample of U.S. adults suggests it increases the risk of many chronic lung illnesses, tooespecially when combined with smoking combustible tobacco.

Most of the media coverage of vaping has focused on the short-term, or acute, health impacts. More than 2,500 cases of e-cigarette, or vaping, product useassociated lung injury (EVALI) have been reported across all 50 states and the District of Columbia, as well as in Puerto Rico and the U.S. Virgin Islands; 54 deaths have been confirmed to date. Black market productscontaining THC (the primary psychoactive ingredient in marijuana were the mostly commonly reported by EVALI patients, buthealth authorities have not ruled out risks of lung injury from other vape products.*

The new research suggests that e-cigarettes may also cause long-term health problems. The study, published this week in the American Journal of Preventive Medicine, found that people who reported using the devices were more likely to develop lung illnesses such as chronic obstructive pulmonary disease (COPD), chronic bronchitis, emphysema or asthma. E-cigarettes have been touted as a harm-reduction method for helping smokers quit, and the new findings could challenge that.

One of the problems that we've had with the whole e-cigarette debate is its asking this abstract question: Are e-cigarettes less dangerous than cigarettes? The answer to that is: if youre a never smoker who never vaped, the e-cigarettes arent as bad as the cigarettes, says study co-author Stanton Glantz, a professor of medicine at the University of California, San Francisco. But in the real world, most adult e-cigarette users are dual [e-cigarette and combustible tobacco] usersand thats worse than [just] smoking.

Like conventional cigarettes, e-cigarettes contain nicotine and various toxic substances that have been shown to disrupt lung function. But e-cigarettes also contain material such as propylene glycol, flavorings such as diacetyl (for a butter taste) and cinnamaldehyde (for cinnamon), as well as heavy metals. Previous studies in animals have shown that exposure to e-cigarette vapor is linked to lung inflammation and depressed immune activity, and repeated exposure appears to cause lung damage that resembles COPD. Most of the studies in humans have been observational, but they have found an association between e-cigarette use and respiratory disease. And a longitudinal study of people with COPD found that smoking e-cigarettes was linked to exacerbations of the disease and a faster decline.

In the new study, Glantz and his U.C.S.F. colleague Dharma Bhatta analyzed data from the Population Assessment of Tobacco and Health (PATH) Study, a longitudinal study of adult tobacco use and health in the U.S. They used data collected from three consecutive time points, or waves, between 2013 and 2016. Respondents were asked whether they currently or previously used e-cigarettes or combustible tobacco (including cigarettes, cigars or cigarillos), or both, as well as whether they had ever been diagnosed with COPD, chronic bronchitis, emphysema or asthma.

Glantz and Bhatta found that people who reported being current or former e-cigarette users at Wave 1 of the study had about a 30 percent higher risk of developing a respiratory disease at Waves 2 and 3, compared with people who had never used the devices. This danger was not as dire as that of current tobacco smokers at Wave 1, who had about a two-and-half-times higher chance of respiratory illness in later waves. But people who used both e-cigarettes and combustible tobacco had the greatest riskthey were 3.3 times as likely to develop a respiratory disease as someone who had never smoked or used e-cigarettes. The findings suggest e-cigarette use is a risk factor for respiratory disease independent of conventional smoking.

Robert Tarran, a professor of cell biology and physiology at the University of North Carolina at Chapel Hill, who was not involved with the paper, says the findings were not all that surprisingbut the fact that this was a longitudinal study strengthens what previous observational ones have found. It basically confirms what people in the field were thinking, which is that vaping isnt good for you, Tarran says. He and his colleagues published a study earlier this year that found that vapers had elevated levels of proteases (proteins that cut up other proteins) in their lungs. Such elevated levelssimilar to those seen in smokerscan lead to emphysema. And just as it can take a long time for the effects of smoking to cause serious disease, we're kind of concerned that with vapers, youre going to see a similar thing, where kids who start vaping now40 to 50 years from now, there's going to be a big epidemic of COPD and lung cancer, Tarran says.

Glantz says he was somewhat surprised that he and Bhatta could detect the increased disease risk in just two yearsthe length of time over which people were tracked in the PATH Study. They also calculated whether switching completely from conventional smoking to e-cigarettes lowered the risk of disease and found that it did. Almost none of the people who used e-cigarettes at Waves 2 and 3 of the study had stopped smoking combustible tobacco, however. Instead smoking both e-cigarettes and combustible tobaccoso-called dual usewas much more common.

Last week, a group of public health researchers published an opinion piece in Science arguing that policies seeking to restrict or ban vaping may be counterproductive, because many adult smokers rely on e-cigarettes to help them quit smoking. But the new findings could undermine this view. The concept that smokers would transition from using cigarettes to e-cigarettes and substantially reduce their health risks is not a crazy idea, says Glantz, who is also a nonsmokers rights activist. But if you look at actual use behaviors, they multiply. And since most people are dual users, youre getting increased harms. In addition, there is the fact that millions of young people who are not regular smokers are getting addicted to e-cigarettes, he adds. (Scientific American reached out to e-cigarette company JUUL Labs and the Vapor Technology Association, a vaping industry trade organization, for comment but did not receive a response.)

The mechanism of lung damage with chronic e-cigarette use is probably different from that behind EVALI, Glantz notes. About 80 percent of those hospitalized in the EVALI outbreak reported vaping THC, and the lung damage in those patients resembled that caused by chemical burns. The U.S. Centers for Disease Control and Prevention has identified vitamin E acetatea type of oil used as a thickening agent in some THC vaping productsas a possible chemical of concern, although the agency is exploring other possible mechanisms.

The PATH Study was focused mainly on tobacco use and did not distinguish between use of nicotine and marijuana e-cigarettes, Glantz says, adding, If had to do it over again, Id include marijuana in the model.

Regardless of whether vaping involves THC or nicotine, though, neither are probably good for the lungs, according to Glantz, adding, As my pulmonologist friends say, lungs are designed to inhale air.

*Editors Note (12/20/19):This article was updated to clarify that most of the products associated with the EVALI outbreak were black-market products.

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Vaping May Increase the Risk of Chronic Respiratory Disease - Scientific American