Vaping could harm heart health, according to scientists who fear e-cigarettes could be as damaging as tobacco smoke.
Two separate studies on e-cigarettes come as health officials try to get to grips with a U.S.-wide outbreak of vaping-related lung illnesses, which have affected over 2,000 people.
Both pieces of research are due to be presented at the American Heart Association's Scientific Sessions 2019, and haven't been published in peer-reviewed journals.
One study involved 476 people aged between 21 and 45. Of the total, 94 didn't smoke, 45 used e-cigarettes, 52 used both e-cigarettes and traditional cigarettes, while 285 smoked tobacco. Those who only used e-cigarettes had lower total cholesterol and higher so-called "bad" LDL cholesterol. Those who both vaped and smoked had lower "good" cholesterol levels.
Study co-author Dr. Sana Majid, a postdoctoral fellow in vascular biology at the Boston University School of Medicine, commented in a statement: "Although primary care providers and patients may think that the use of e-cigarettes by cigarette smokers makes heart health sense, our study shows e-cigarette use is also related to differences in cholesterol levels. The best option is to use FDA-approved methods to aid in smoking cessation, along with behavioral counseling."
In the other study, researchers measured the heart blood flow of 19 smokers aged between 24 to 32 years old, immediately after they vaped, or smoked a regular cigarette. The team also used a machine to document the participants' coronary vascular function while the volunteers were resting, and after completing a handgrip exercise which mimicked physiological stress.
The team found the blood flow increased a little after participants smoked tobacco and decreased after stress. In vapers, blood flow increased after inhaling and after stress.
Co-author of the second study, Dr. Florian Rader, medical director of the Human Physiology Laboratory and assistant director of the Non-Invasive Laboratory, Smidt Heart Institute, Cedars-Sinai Medical Center, Los Angeles, explained in a statement: "These results indicate that e-cig use is associated with persistent coronary vascular dysfunction at rest, even in the absence of physiologic stress."
Dr. Susan Cheng, director of Public Health Research, also of Cedars-Sinai Medical Center, said in a statement her team was surprised to find the heart's blood flow was reduced at rest, even in the absence of stress, after vaping.
She suggested health care providers helping patients to stop using nicotine products might want to "consider the possibility that e-cigs may confer as much and potentially even more harm to users and especially patients at risk for vascular disease."
Experts in the field not involved in the studies told Newsweek the findings could indicate that switching to vaping from regular smoking may not protect a person from heart problems.
Dr. J. Taylor Hays, an expert in tobacco dependence and Director of the Mayo Clinic Nicotine Dependence Center, highlighted that these are some of the first studies to look at the physiological impact of e-cigarettes on coronary circulation and cardiovascular risk factors like cholesterol.
He said the blood flow study tells us that vaping long-term "does have a measurable negative impact on coronary circulation."
The impacts measured are known to be precursors to coronary atherosclerosis, where plaque builds up in the arteries, and coronary heart disease, he said.
"This means that people who switched to electronic cigarettes from traditional tobacco cigarettes may not see a decline in their risk of coronary heart disease," he warned.
The other study "also shows that these coronary disease risk factors are negatively influenced with the use of electronic cigarettes in a fashion similar to traditional tobacco cigarettes.
"This reinforces the possibility that encouraging smokers to switch to electronic cigarettes may not reduce their risk for cardiovascular complications," he said.
Hays said he was most surprised that regular e-cigarette users experienced a significant decline in heart blood flow after vaping, whereas tobacco users did not have a similar decline until after the stress test.
"This suggests that electronic cigarettes may have much greater negative impact on coronary disease risk [than has ever] been imagined, and possibly comparable to tobacco cigarettes," he said.
However, Hays said the studies were limited by the small numbers of participants, and that the subjects were not been followed up in the long term, meaning we don't yet know if they will develop coronary disease. That would take many years, he said. Also, the results haven't been replicated by other researchers.
Commenting broadly on vaping, he continued: "These studies call into question this assertion of certainty about the safety of electronic cigarettes" and leave experts in a "quandary about how to advise tobacco cigarette smokers."
Asked whether vaping is as bad or worse for the heart as regular tobacco smoking, he said: "There is so little information about the long-term health effects of electronic cigarette use, including cardiovascular disease, and such a wealth of information about the serious adverse cardiovascular disease caused by tobacco smoking, that right now we would say tobacco smoking is more harmful than electronic cigarette use."
"But these new studies give us reason to think that with enough time we may start seeing similar cardiovascular effects from chronic electronic cigarette use as we had seen from traditional cigarette use. Only time and much more research will tell."
Maciej L. Goniewicz, associate professor of oncology at Roswell Park Comprehensive Cancer Center told Newsweek that e-cigarettes "contain nicotine and emit particulates and several toxicants that may negatively affect heart and blood vessels of users."
He said the cholesterol study shows those who use e-cigarettes and combustibles had "no improvement in health outcomes."
"If [a] smoker seriously considers e-cigarette as a substitute product for combustible cigarettes, he or she should switch completely," he said.
"I think we need more data on the potential long-term consequences of nicotine vaping, not only in adult ex-smokers, but also in young regular vapers," he continued. "Since e-cigarettes are also commonly used to deliver other substances, particularly THC and CBD (active substances in cannabis), studies should also look at potential health effects of different drugs inhaled with e-cigarettes."
Goniewicz argued it is not possible to directly compare the harm from smoking versus vaping based on present findings.
"I think the scientific evidence still strongly suggests that smokers who switch completely to e-cigarettes may reduce their health risk," he said.
"However, the transition from combustible to electronic cigarettes needs to be complete. On the other hand, there is growing evidence of potential negative health consequences of regular vaping in young people who have never smoked tobacco cigarettes."