Nicotine in e-cigarettes causes blood to clot, research shows.
Some people who smoke e-cigarettes have damage to their blood vessels.
And their heart rate and blood pressure increase.
The effects are similar to the effects of traditional smoking.
Researchers have now warned that people who often use e-cigarettes with nicotine are at risk of heart attack or stroke.
A Swedish study of 22 young smokers was presented at a European conference.
“This study adds to the growing evidence of the harmful effects of e-cigarettes,” said Jonathan Griff, a professor at Queen Mary University of London.