E-cigarettes impair blood vessel function as much as conventional cigarettes do in rats

When e-cigarettes first appeared on the market, they were sold as a safer alternative to smoking cigarettes. And while e-cigarettes do have fewer cancer-causing chemicals than cigarettes do, a growing body of evidence suggests that the devices may not avoid other harmful effects of smoking.

Now, a study led by Matthew L. Springer at the University of California, San Francisco, finds that, in rats, puffs from e-cigarettes and cigarettes comparably impair the function of blood vessels, which is a predictor of cardiovascular disease such as stroke or heart attack. Additionally, the researchers found that Juul e-cigarettes deliver substantially higher amounts of the addictive substance nicotine than cigarettes and previous generation e-cigarettes do per puff (Tob. Regul. Sci. 2020, DOI: 10.18001/TRS.6.1.4).

Springer and colleagues evaluated three types of cigarettes: Virginia tobacco flavored Juul e-cigarettes, a tank style e-cigarette, and Marlboro Red cigarettes. For each type of cigarette, a group of eight anesthetized animals received ten puffs over 5 minutes. The team also tested puffs of air as a control.

Using an ultrasound method previously developed by Springer’s lab, the researchers looked at the rats’ arterial flow-mediated dilation (FMD), a hallmark of blood vessel function, after inhalation. FMD is a measure of blood vessels’ ability to stretch in response to the flow of blood. They observed similar impairment in FMD among rats that had inhaled Juul e-cigarettes, tank style e-cigarettes, and cigarettes.

While dysfunction in FMD does not necessarily lead to cardiovascular disease, it’s used as a predictor for disease, says Mark Olfert, who studies cardiovascular health at West Virginia University. Poor FMD is one of many factors, such as genetics or diet, he says, that put people at risk for cardiovascular diseases such as stroke or hardening of the arteries.

“This paper is really important because it’s essentially showing that blood vessels can’t tell the difference whether the animals, and presumably people, are smoking a cigarette or an e-cigarette. The damage and harm that’s being caused looks to be the same,” Olfert says.

He says early animal studies like this one are crucial because it may be decades before we see the negative health effects from e-cigarettes, which have only been around for about 13 years. “[Animal studies] give us insight into the long-term responses that we can expect to see in humans,” he says, adding that previous inhalation research has shown that rodents are a good predictive model for the effects of smoking on humans.

The team also found, by measuring nicotine levels in the rat’s blood serum, that Juul e-cigarettes deliver about five times as much nicotine as cigarettes and eight times as much as previous tank-style e-cigarettes do in the same number of puffs. But it’s difficult to tell if the higher levels of nicotine delivery translates to humans because the number of times a person inhales can differ, Springer says.

He points out that whereas experienced adult smokers are more likely to stop inhaling once they’ve achieved the nicotine level they want, younger smokers may not know their limits, which means they could be exposed to much higher levels of the addictive substance. Juul e-liquids contain the salt form of nicotine, which makes the vapor less harsh and easier to inhale and is thought to contribute to their popularity among young people.

“I don’t think anyone doing this research would argue that e-cigarettes are exactly as bad as cigarettes are,” Springer says. “The take home lesson is that it’s unwise to assume that e-cigarettes are OK.”