WEDNESDAY, Feb. 4, 2015 (HealthDay News) -- New research with mice shows that electronic cigarette vapor weakens the immune system in the lungs and contains some of the same harmful chemicals found in tobacco cigarettes.
E-cigarettes are growing in popularity in the United States, partly because many people think they aren't as dangerous as tobacco cigarettes, the researchers said.
"Our findings suggest that e-cigarettes are not neutral in terms of the effects on the lungs," study senior author Shyam Biswal, a professor of environmental health sciences at the John Hopkins Bloomberg School of Public Health, said in a Hopkins news release.
Although animal tests don't necessarily apply to humans, the findings suggest that smoking e-cigarettes might make users susceptible to lung infections, the researchers said.
"We have observed that they [e-cigarettes] increase the susceptibility to respiratory infections in the mouse models," Biswal said. "This warrants further study in susceptible individuals, such as COPD (chronic obstructive pulmonary disease) patients who have switched from cigarettes to e-cigarettes or to new users of e-cigarettes who may have never used cigarettes."
The researchers exposed one group of mice to an amount of e-cigarette vapor that approximated human exposure to e-cigarette vapor for two weeks. A control group of mice was just exposed to air.
The mice also were exposed either to bacteria that cause pneumonia and sinusitis or to an influenza-causing virus, or to neither. Those exposed to e-cigarette vapor were much more likely to have weakened immune responses to the bacteria and virus, and some of those mice died as a result, the researchers said.
"E-cigarette vapor alone produced mild effects on the lungs, including inflammation and protein damage," study lead author Thomas Sussan, an assistant scientist in the department of environmental health sciences at the Bloomberg School, said in the news release.
"However, when this exposure was followed by a bacterial or viral infection, the harmful effects of e-cigarette exposure became even more pronounced. The e-cigarette exposure inhibited the ability of mice to clear the bacteria from their lungs, and the viral infection led to increased weight loss and death indicative of an impaired immune response," he explained.
The study, published Feb. 4 in the journal PLoS One, could serve as a model for future studies on the health effects of e-cigarettes, the researchers said.
American teens' use of e-cigarettes is greater than their use of tobacco cigarettes, according to the U.S. government. More than one-quarter million teens who said they never smoked a cigarette reported using e-cigarettes in 2013.
According to the study authors, e-cigarettes contain less nicotine than cigarettes, but actual nicotine intake is similar for e-cigarette users and regular cigarette smokers.
Last year, the U.S. Food and Drug Administration said it planned to start regulating e-cigarettes.
The U.S. National Institute on Drug Abuse has more about electronic cigarettes.