We’ve long known about the negative effects of cigarette smoking on health. In relation to cardiovascular diseases (CVD) — the leading cause of death in the U.S. and the world — cigarettes are known to contribute to increased susceptibility due to their effects on the heart, lungs, and blood vessels. These effects include inducing oxidative stress and inflammation, elevating blood pressure and sympathetic nervous system activity, and causing cardiac dysfunction.
The recent decade has brought a rise in the popularity of a supposedly “safer” alternative to tobacco cigarettes — the electronic cigarette (e-cigarette). While some data suggest e-cigarettes are safer since they contain fewer toxic chemicals, there are still significant health risks associated with e-cigarettes. They’re far from a harmless substitution.
Since they are a relatively recent invention, we don’t have a lot of scientific data on the effects of e-cigarettes on cardiovascular function, especially the long-term effects, since this would require follow up studies on humans who have used e-cigarettes for a considerable time period.
However, these studies are urgently needed if we want to understand the potential implications of chronic e-cigarette use and the impact on cardiovascular and other diseases. If e-cigarettes are truly safer than regular cigarettes, this information could be highly valuable. If they are similar or worse than traditional cigarettes, even more so.
A new study published in the American Journal of Physiology: Heart and Circulatory Physiology, took on the task of examining the chronic effects of electronic cigarette exposure. Perhaps even more interesting is that they compared e-cigarette exposure to traditional cigarette smoke exposure, as well as the effects of different amounts of nicotine present in e-cigarettes.
Brief study methods
This study was conducted in mice, who were separated into 5 different study groups:
- One group was exposed to normal air (control group)
- One group was exposed to traditional cigarette smoke
- Three groups were exposed to electronic cigarettes containing: 0 mg/ml of nicotine, 6 mg/ml of nicotine, and 24 mg/ml of nicotine
Each group of mice were exposed to their assigned condition 5 times per week, starting at 20-weeks of age. Exposure continued until the mice were 60 weeks of age — a timeframe designed to mimic someone taking up e-cigarette use at age ~15 and continuing until they were aged 60 (i.e. ~40 years of exposure).
At 16, 24, 32, and 60 weeks of exposure, measures were taken that included blood pressure, blood vessel (endothelial) function, cardiac function, cardiac structure, and levels of reactive oxygen species (ROS) in blood vessels and the heart. Levels of plasma cotinine — a metabolite of nicotine — were also measured in the mice after a single exposure to determine the effects of regular and e-cigarettes on nicotine levels.
Below are some of the main findings of the study.
- Blood pressure significantly and progressively increased throughout the 60-week exposure period in all electronic cigarette exposure groups and the traditional cigarette exposure groups
- Vascular function was impaired in the electronic cigarette and traditional cigarette groups, which was observed as early as 16-weeks into the exposure period
- Left-ventricular mass progressively increased in electronic cigarette and traditional cigarette groups throughout the 60-week exposure period
- Both the electronic cigarette and traditional cigarette groups had increased heart weight at 60-weeks
- Thickness of the aortic wall was increased in all of the cigarette exposure groups, with greater changes in the traditional cigarette group vs. the lower dose nicotine electronic cigarette groups
- The receive oxygen species (ROS) molecule superoxide was increased in the arteries of mice exposed to both cigarettes; with the highest levels in the traditional cigarette and high-dose nicotine e-cigarette groups
There are some very novel and innovative findings here that shed light on the comparable effects of traditional and e-cigarettes on cardiovascular structure and function. Overall, I think these findings, which support those of other studies, are pretty damning for the “safety” claim that is made about e-cigarettes. These results would suggest they are no better than regular tobacco cigarettes.
Some other neat conclusions from this study relate to the independent effects of nicotine on cardiovascular function. While all types of e-cigarettes exerted negative effects on most of the study measures, these effects seemed to be increased in a dose-response manner with nicotine.
The authors go into some detail on how nicotine affects the cardiovascular system, potentially affecting ROS production and sympathetic nervous system activity, both of which play a role in cardiovascular impairment and disease.
Along with the other toxic chemicals that are produced during e-cigarette use, nicotine could perhaps augment adverse cardiac, vascular, and autonomic effects, with higher doses being worse. Nicotine appears not just to be highly addictive, but dangerous for the heart.
The obvious caveat here is that these findings were in rodents, not humans. However, I do think that the specific protocol and timeline used did a fair job of trying to make these results “generalizable” to human cigarette consumption.
The plasma levels of nicotine (cotinine) measured in the mice were comparable to those seen in humans after cigarette use. Furthermore, as mentioned earlier, the authors used an age of onset of smoking that represented ~15 years in humans, and the exposure period ended at a “human age” of 60. While not a perfect translation, this model could be used to represent a “lifelong user.”
The introduction of e-cigarettes might have done a fair job of reducing the incidence of cigarette smoking, but has this come with a cost? E-cigarettes have allowed younger and overall a larger number of people to take up a “smoking” habit (who otherwise might not have), and this could have wide-ranging consequences in the coming decades. How many never users took up an e-cigarette smoking habit because they perceived it as “safe?”
As we gather more data like those presented here, I think that we will eventually come to similar conclusions about e-cigarettes that we did with smoking decades ago. Lung cancer is only part, if not a less-urgent cause for concern when it comes to smoking. Electronic or not, cigarettes are a clear health hazard.
El-Mahdy MA, Mahgoup EM, Ewees MG, Eid MS, Abdelghany TM, Zweier JL. Long-term electronic cigarette exposure induces cardiovascular dysfunction similar to tobacco cigarettes: role of nicotine and exposure duration. American Journal of Physiology-Heart and Circulatory Physiology. 2021;320(5):H2112-H2129.