Scientists have urged caution over a study linking nicotine vaping with impaired blood vessel function and lower fitness in young adults, warning that its small sample cannot establish whether vaping causes cardiovascular damage.
The study, led by Manchester Metropolitan University (MMU) researchers and published in JAMA Cardiology, found that young adults who vaped had lower average measures of vascular function and cardiorespiratory fitness than people who had never used tobacco or nicotine products.
However, independent experts questioned whether the findings could be attributed to vaping itself, highlighting the study’s small sample, differences between participants and cross-sectional design.
Dr Maxime Boidin, senior lecturer in cardiac rehabilitation at MMU and the study’s lead author, said the results suggested that regular nicotine vaping was associated with changes in vascular function and exercise capacity, even among otherwise healthy young adults.
He stressed, however, that the findings did not mean vaping was as harmful as smoking overall.
“If you smoke, switching completely to nicotine vapes markedly reduces the level of exposure to harmful chemicals. If you don’t smoke, you should never vape,” Boidin said.
The researchers said further longitudinal studies were needed to determine whether the observed differences lead to cardiovascular disease later in life.
What the study found
The research assessed 58 healthy adults with an average age of 26, divided into three groups: 17 exclusive nicotine vape users, 19 cigarette smokers and 22 people who had never used tobacco or nicotine vapes.
Researchers measured blood vessel function using flow-mediated dilation (FMD) and carotid artery reactivity (CAR), alongside cardiorespiratory fitness during maximal exercise testing.
Average FMD was 5.5% among vape users and 4.4% among smokers, compared with 8.3% among those who had never smoked or vaped. CAR was also lower in both nicotine-use groups than among nicotine-naive participants.
Vape users had lower peak oxygen uptake, a measure of cardiorespiratory fitness, than those who had never used nicotine products. Measures of ventilation and cardiac output were lower in both the vaping and smoking groups.
The researchers found no significant differences in lung function between the groups.
MMU said the vaping group comprised people who vaped but had never regularly smoked, meaning the findings were relevant to the potential risks of taking up vaping rather than to smokers switching away from tobacco.
Boidin said the degree of vascular impairment observed among vapers was not substantially different from that seen in smokers on the specific measures examined. He cautioned that this did not establish that vaping and smoking carry equivalent overall health risks.
“While our study does not prove that vaping causes cardiovascular damage, it does show that young adults who vape regularly had impaired blood vessels and lower cardiorespiratory fitness than their peers who had never used nicotine products,” he added.
The study’s authors acknowledged that its small sample, local volunteer recruitment and cross-sectional design meant it could not establish cause and effect or rule out pre-existing differences between participants.
Independent experts question conclusions
Dr Harry Tattan-Birch, senior research fellow in the Department of Behavioural Science and Health at University College London (UCL), said the study’s design did not support firm conclusions about the effects of vaping.
“This small study draws conclusions that its design cannot support,” he said.
“It compares just 17 vapers, 19 smokers and 22 people who use neither at a single point in time, without adequately accounting for other differences between these groups that could explain the findings. Therefore, we cannot know whether the findings reflect effects of
Tattan-Birch also challenged any suggestion that the results undermined the evidence for vaping as a less harmful alternative for people who smoke.
“This is a serious overinterpretation. Failing to find a statistically significant difference between just 17 vapers and 19 smokers does not mean their effects are equivalent. With such small samples, even substantial differences could easily be missed,” he noted.
Dr Katie East, associate professor in public health at Brighton and Sussex Medical School, raised concerns about the recruitment criteria and participants’ smoking histories. She said the groups differed in the frequency and intensity of nicotine use, while small sample sizes and baseline differences made it difficult to draw reliable conclusions.
“Currently in Great Britain, only 29% of adults accurately perceive vaping as less harmful than smoking. Overinterpreting such small-scale observational studies can further fuel public misperceptions of vaping, and risks discouraging adults who smoke from transitioning to a less harmful product,” East warned.
Professor Peter Hajek, professor of clinical psychology and director of the Health and Lifestyle Research Unit at Queen Mary University of London, suggested that the results could reflect differences in lifestyle and fitness that existed before participants began using nicotine products.
“The authors correctly acknowledge that the study cannot establish causality, but the press release hints at harms of vaping, something the study did not show,” he commented.
Professor Lion Shahab, professor of health psychology and co-director of UCL’s Tobacco and Alcohol Research Group, also described the findings as exploratory.
He highlighted differences in physical activity between the groups, the potential influence of other factors and uncertainty about the clinical significance of the vascular measurements. These measures are not direct indicators of cardiovascular disease, he said, and their ability to predict future problems in otherwise healthy people is not well established.
Shahab called for larger studies following participants over time to establish whether vaping itself affects vascular function and fitness, and whether any observed changes have meaningful long-term consequences.
The MMU study follows earlier research led by the university that reported reduced fitness among young adults who smoke or vape.
The latest findings also bring renewed scrutiny to how research led by Boidin is communicated. In March 2025, tobacco policy analyst and former Action on Smoking and Health (ASH UK) director Clive Bates criticised the MMU academic over publicity surrounding an earlier, then-unpublished vaping study.
In an open letter, Bates accused Boidin of generating sensationalist media coverage based on incomplete research, warning that claims comparing vaping with smoking could deter smokers from switching to a less harmful alternative.
The earlier criticism concerned the publicity surrounding that study and does not, in itself, establish whether the findings of the current research are valid.
The latest research was funded by a Cardiovascular Research Grant from Manchester Academic Health Science Centre – Health Innovation Manchester.