Researchers studied more than 400 men and women aged between 21 and 45 made up of non-smokers, cigarette smokers, e-cigarette users and people who both smoked and vaped.

The team studied measures of blood vessel function in e-cigarette and dual users who had been using e-cigarettes for at least three months. Author Jessica Fetterman, assistant professor of medicine at Boston University School of Medicine, said that stiffening of the arteries can contribute to heart disease. She added: “Many people believe e-cigarettes are safer than combustible cigarettes.