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"This is the first study to look at these cardiac risk factors in habitual e-cigarette users. The results were a bit surprising, since it is widely believed that e-cigarettes are less harmful than tobacco cigarettes," said study co-author Dr. Holly Middlekauff. She is a professor with the division of cardiology at the University of California, Los Angeles.
Instead, she said, "we found the same types of abnormalities in our e-cigarette users that are reported in tobacco cigarette smokers, and these abnormalities are associated with increased cardiac risk."
Middlekauff stressed that the study only shows an association, not a cause-and-effect link, between e-cigarette use and increased heart risks. And, because the study did not include traditional cigarette smokers, "we cannot say if the changes are less severe in the e-cigarette users compared to age-matched tobacco cigarette smokers," she added.
"All we can conclude is that e-cigarette use has real physiologic, adverse effects," she said. "They are not harmless."
Electronic cigarettes first became available in the United States in 2006. Since then, their popularity has skyrocketed. The U.S. National Institute on Drug Abuse estimates that more than 250 brands of e-cigarettes are now sold, the researchers said.
All the e-cigarette users in the study were healthy and between the ages of 21 and 45. The e-cigarette users had been vaping almost daily for a minimum of one year. None of the participants smoked tobacco cigarettes.
All the e-cigarette users and nonusers had blood tests and heart rate variability testing, to measure various aspects of heart behavior.
The result: E-cigarette users had a higher risk for oxidative stress, in which so-called "free radical" molecules produced through breathing start to reach potentially harmful levels, the researchers said.
E-cigarettes were also found to have an increased risk for a rise in "cardiac sympathetic activity," stemming from a boost in the level of hormones produced by the adrenal gland. Ultimately, this can give rise to an increased heart rate and higher blood pressure, the researchers said.
The findings were published online Feb. 1 in the journal JAMA Cardiology.
Middlekauff said she and her colleagues are now comparing the heart effects of chronic e-cigarette use to chronic tobacco cigarette use.
It's still unclear why e-cigarettes may increase the risk for heart trouble, she said.
"I would speculate that inhaled nicotine is the culprit," Middlekauff said. "Nicotine is the most biologically active component in e-cigarette aerosol, and is an airway irritant. Nicotine increases adrenaline levels, and may activate a number of adverse systems that are harmful in the long run."
Aruni Bhatnagar is a professor of medicine with the University of Louisville's division of cardiovascular medicine. He said that, although e-cigarettes expose users to fewer chemicals than traditional cigarettes, "they contain some residual components, particularly nicotine, that may present a not insignificant problem.
"So, I would say that what is being reported here is important, but not really startling," said Bhatnagar, who cowrote an editorial accompanying the study and serves as director of the American Heart Association's Tobacco Center.
Gregory Conley, president of the American Vaping Association, criticized the study findings.
"This study, like so many performed by researchers looking to generate headlines, fails to compare the effects of vaping nicotine-containing liquid with other activities, such as smoking cigarettes, using non-nicotine liquid or drinking coffee," Conley said.
"Even if such comparisons were used, the value of this paper is limited, as it is not exactly breaking news that nicotine has short-term impacts on the cardiovascular system," he said.
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