Vapers who have also smoked tobacco may be at greater risk of stroke compared to people who only smoke cigarettes, new research suggests.
Those who used both at the time of the study were almost two times (1.83) more likely to have a stroke, compared to those who only smoked cigarettes at the time, according to the study.
And they were nearly three times (2.91) more likely than non-smokers to have a stroke, the research published in the American Journal of Preventive Medicine suggests.
Compared with non-smokers, sole e-cigarette smoking was not linked to significantly different odds of stroke.
However, if participants had former or current cigarette use, odds of stroke were significantly increased even when compared to current sole cigarette use, scientists say.
But Dr Lion Shahab of University College London, cautioned that it was not clear whether dual use of e-cigarettes, or switching to e-cigarettes from cigarettes, was a result of stroke or preceded it.
The study calculated the adjusted odds ratios (AORs) for cerebrovascular events among the smokers.
It suggests the AOR for stroke among those with current sole tobacco use was 1.59, and current vapers who were former cigarette users had an AOR of 2.54.
The odds were almost three times higher in current dual users versus non-smokers.
Compared with current tobacco smokers, vapers had lower odds of stroke (0.43), the research suggests.
They suggest that switching from tobacco to e-cigarettes does not confer stroke benefits.
Lead investigator Tarang Parekh, department of health administration and policy, at George Mason University in America, said: “It’s long been known that smoking cigarettes is among the most significant risk factors for stroke.
“Our study shows that young smokers who also use e-cigarettes put themselves at an even greater risk.
“This is an important message for young smokers who perceive e-cigarettes as less harmful and consider them a safer alternative.
“We have begun understanding the health impact of e-cigarettes and concomitant cigarette smoking, and it’s not good.”
He added that the findings indicate an “additive harmful effect of e-cigarettes on smokers’ blood vessels, hearts and brains”.
Factors weighed in this ratio included frequency of use, demographic factors, hypertension, diabetes, and cholesterol levels, body mass index, physical activity, and alcohol use.
The researchers say it is important to analyse long-term effects of e-cigarette smoking on cerebrovascular metabolism before completely dismissing a higher stroke risk.
This study also did not find any clear benefit from using e-cigarettes if users are switching from combustible cigarette smoking.
Investigators used data from the 2016-2017 Behaviour Risk Factor Surveillance System (BRFSS), a national annual, cross-sectional health survey conducted jointly by the Centres for Disease Control and Prevention and all US states and territories.
They analysed responses on cigarette and e-cigarette use from 161,529 participants aged 18 to 44 years old.
Dr Shahab, senior lecturer in epidemiology and public health at UCL, said: “It is entirely possible that the group of current or former smokers took up e-cigarettes precisely because they had a health scare, which would result in the observed association.”
He added: “It is entirely possible that dual users chose to use e-cigarettes in addition to cigarettes because they are more dependent, as has been found in other studies, which would suggest that over their lifetime this group of people may have been exposed to more harmful substances from cigarette smoking, increasing their risk of stroke.
“While this paper highlights the need to continue studying the potential health effects of e-cigarette use, the results should be interpreted with caution as the observed associations may be simply due to unmeasured confounding and reverse causality.”