The science on e-cigarette ‘juice’ is still far from settled.

A scientist from Brown University is claiming that prolonged exposure to nicotine, even delivered by methods other than cigarettes, may increase the risk of developing a potentially fatal heart condition.

It’s the latest research to question the safety of e-cigarettes, a popular substitute for smoking tobacco cigarettes, which are known to be harmful.

Chi-Ming Hai unveiled his findings at the American Society for Cell Biology’s annual meeting in New Orleans. The presentation stems from work published last year in the journal Vascular Pharmacology.

Hai studied how nicotine and cigarette smoke extract stimulate the formation of rosettes on the surface of cells. The rosettes act like drills to bore through a scaffolding that protects vascular cells in the heart.

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The result can be atherosclerosis, or hardening of the arteries, a common cause of heart attacks. The newly reported research, for which Hai only provided an abstract, shows that the process occurs during nicotine administration, even without cigarette smoke.

Hai subjected rat and human vascular smooth muscle cells to nicotine for six hours. He said that the nicotine stimulated the rosettes to bore through the cells’ defenses.

Hai described atherosclerosis as a sort of “cancer of blood vessels” which leads to plaque build-up and clogged arteries.

“Cigarette smoke contains thousands of chemicals, but nicotine is the major chemical that causes cigarette addiction,” Hai said in a statement to Healthline.

“In my opinion, if taking nicotine for a short time can lead to complete cessation of smoking, e-cigarette included, then it will be beneficial to take nicotine for a short time as a bridge to smoking cessation,” he added. “However, our data suggest that long-term consumption of nicotine by e-cigarette smoking is likely to increase the risk of developing atherosclerosis by stimulating invasion of vascular smooth muscle cells.”

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Carl Phillips, scientific director for the Consumer Advocates for Smoke-Free Alternatives Association (CASAA), dismissed the research as “nonsense.”

“There is some pretty good research going on about why exactly cigarette smoke causes heart disease, which was substantially not understood,” he told Healthline. “But any such research that reaches the conclusion that the nicotine without smoke causes such disease is clearly wrong.”

Elaine Keller, president of the CASAA, pointed to other recently published research that she said shows outcomes in the “real world” as opposed to a laboratory. One study showed that smokers put on nicotine replacement therapy after suffering an acute coronary event like a heart attack or stroke had no greater risk of a second incident within one year than those who were not.

Another study, conducted in Sweden, showed no greater risk of heart attack among men who chewed tobacco than among those who didn’t.

Jed Rose, a Duke University professor of psychiatry and behavioral science, told Healthline that the levels of nicotine administered in Hai’s 2012 study were about 10 times higher than what an average cigarette smoker would inhale.

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Dorothy Hatsukami, a psychiatry professor at the University of Minnesota, is currently recruiting volunteers to study the effects of e-cigarettes. She plans to study 25 people who smoke with the new devices and 25 people who smoke them in addition to tobacco cigarettes.

For starters, she wants to know the effects of the chemicals inhaled in the e-cigarette vapor. The main ingredient—propylene glycol—is already used in some food products and toiletries in the U.S. In a 2006 review of the substance, the FDA found no research to suggest a public health hazard when used at its current levels or in the future.

But with the burning popularity of e-cigarettes, the FDA had been expected to issue new guidelines this year. They have not, possibly as a result of the government shutdown.

The devices are so new there is virtually no regulation at all. “We’re really at the beginning stages of understanding what the potential health impact might be,” Hatsukami told Healthline. “There could be public health benefits, certainly they are less toxic than cigarettes, but they may lead to other public health harms.”

She likened the current e-cigarette environment to the ‘Wild West.’

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“Vapers,” as e-cigarette smokers call themselves, find the fuss over their new fix frustrating. Todd Smith owns a vaping supply store in Davenport, Iowa called the Vaporosity Shop. He has franchised his business, which began with one location, to four stores in two states in just five months.

The vapor in the e-cigarettes at Vaporosity stores comes from a “juice” made by the husband of a franchisee who is a high school science teacher, Smith said. The flavored liquid includes nicotine and propylene glycol, as with most e-cigarettes.

He told Healthline he is among the millions of Americans who have quit smoking tobacco cigarettes, proven to be deadly, by switching to vaping. He scoffs at efforts to demonize the products and at new initiatives to ban these devices in public.

“We don’t lose our taste buds when we become adults,” he said, referring to e-cigarette flavors like bubble gum and cotton candy. “And if they’re going to ban e-cigarettes, then they’d better ban fog machines at Halloween.”

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