Scientists have discovered that certain vaping flavours could put users at a higher risk of having a heart attack or a stroke.
Research performed at the Stanford University School of Medicine discovered that - among several flavours tested - cinnamon and menthol flavours are the most damaging.
The study found that blood vessels, when exposed to vape fluid, started to exhibit 'significantly increased levels' of cell death and DNA damage.
They also discovered that this varies from flavour to flavour.
Among the types of e-liquid they tested were fruit, sweet tobacco, menthol, caramel and vanilla, butterscotch, cinnamon, and tobacco. They also tested e-liquids with varied nicotine content.
They looked at ones with six milligrams of nicotine, zero milligrams, and eighteen milligrams.
After their research, they concluded that cinnamon and menthol flavours are the worst for your cells and DNA.
Professor Joseph Wu, the senior author of the study, said: "Until now, we had no data about how these e-liquids affect human endothelial cells.
"This study clearly shows that e-cigarettes are not a safe alternative to traditional cigarettes.
"When we exposed the cells to six different flavours of e-liquid with varying levels of nicotine, we saw significant damage."
Their study showed that for the most part, the liquids were 'moderately toxic' to cells, whereas there was 'significantly increased' cell damage shown by the cinnamon and menthol liquids.
That includes the variations without nicotine.
It has also been suggested that several types of e-liquid flavour can harm lung function.
The findings, which were published in the Journal of the American College of Cardiology, purported that caramel and popcorn flavours can also disrupt cell growth. Neither cinnamon and caramel and vanilla flavours were as bad at disrupting cell growth, but both showed several signs of inflammation and endothelial dysfunction.
As part of the same study, the scientists looked into the amount of nicotine that is absorbed into the blood between those who smoke traditional cigarettes and those who vape.
After 10 minutes of smoking, the nicotine levels were comparable between both.
Study co-lead Dr Won Hee Lee, who is an assistant professor at the University of Arizona, said: "When you're smoking a traditional cigarette, you have a sense of how many cigarettes you're smoking.
"But e-cigarettes can be deceptive. It's much easier to expose yourself to a much higher level of nicotine over a shorter time period.
"And now we know that e-cigarettes are likely to have other significantly toxic effects on vascular function as well.
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"It's important for e-cigarette users to realise that these chemicals are circulating within their bodies and affecting their vascular health."
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