Small study finds electronic cigarettes have harmful physiologic effects

The use of electronic cigarettes has increased significantly since they were first marketed in the U.S. in 2006. Manufacturers have promoted the handheld devices as safe alternative to tobacco cigarettes, although scientific data about electronic cigarettes are limited.

A new, small cross-sectional study, though, found that electronic cigarette users had sympathetic predominance and increased oxidative stress, which are associated with increased cardiovascular risk. However, the researchers noted further research was necessary to determine the potential adverse health effects of electronic cigarettes.

Lead researcher Roya S. Moheimani, BS, of the University of California, Los Angeles, and colleagues published their results online Feb. 1 in JAMA Cardiology.

The researchers noted that electronic cigarettes are handheld devices that deliver nicotine, flavorings and a humectant into the mouth and lungs when puffed. They do not contain tobacco.

“It is too large a step to say that these negative effects are proof that people are going to die early because they used e-cigarettes,” Joep Perk, MD, a European Society of Cardiology cardiovascular prevention spokesperson, said in a news release. “To prove this you have to put people on e-cigarettes for 10 to 15 years and see how many die early—a study that will not be done for ethical reasons. The weakness of all studies in this field is that they are observational and small, and they look at indicators of vascular wall damage rather than incidence of cardiovascular disease or death.”

The study included participants who were between 21 and 45 years old and used electronic cigarettes most days for at least one year. The participants drank two or fewer alcoholic drinks per day, did not smoke cigarettes, did not use illicit drugs, had no known health problems, did not take prescription medications and were not exposed to secondhand smoke or use nicotine replacement therapies.

In all, 23 participants were self-identified habitual electronic cigarette users and 19 were self-identified non-tobacco cigarette, non-electronic cigarette users.

The researchers measured the participants’ heart rate variability as well as three parameters of oxidative stress: low-density lipoprotein oxidizability, high-density lipoprotein antioxidant/anti-inflammatory capacity and paraoxonase-1 activity.

The mean age of participants was 27.6 years old, while 35 percent were women and 35 percent were white.

Electronic cigarette users had a significant decrease in the high-frequency component of heart rate variability and a significant increase in the low-frequency component of heart rate variability as well as the low frequency to high frequency ratio. The high-frequency component indicated vagal activity, the low-frequency component indicated a mixture of vagal and sympathetic activity and the ratio of low to high frequency reflected the cardiac sympathovagal balance, according to the researchers.

Electronic cigarette users also had a significant increase in low-density lipoprotein oxidizability, although there was no differences between the groups with regards to high-density antioxidant/anti-inflammatory capacity and paraoxonase-1 activity.

“These findings are important for 2 reasons: first, because both increased cardiac sympathetic activity and increased oxidative stress are known mechanisms by which tobacco cigarettes increase cardiovascular risk, these findings have critical implications for the long-term cardiac risks associated with habitual e-cigarette use,” the researchers wrote. “Second, these findings mandate a re-examination of aerosolized nicotine and its metabolites. Nicotine, which is the major bioactive ingredient in e-cigarette aerosol, with its metabolites, may harbor unrecognized, sustained adverse physiologic effects that lead to an increased cardiovascular risk profile in habitual e-cigarette users.”

The study had a few limitations, according to the researchers, including that they could not be certain that one or more participants consumed tobacco products. They also did not screen for marijuana or other drug exposures. In addition, they noted that the relative effect of tobacco cigarettes compared with electronic cigarettes on autonomic balance and oxidative stress was unknown.

“On the basis of these studies, we can conclude that habitual e-cigarette use is associated with physiologic effects,” the researchers wrote. “Nonetheless, we cannot confirm causality on the basis of this single, small study; further research into the potential adverse cardiovascular health effects of e-cigarettes is warranted.”