London, Sep 11 (IANS) Vaping e-cigarettes with nicotine may cause stiffening of the arteries in humans and that may increase the risk of heart attacks and strokes in later life, researchers have found. Researchers conducted a study that included young adults -- average age of 26 -- with no history of electronic cigarette use who identified themselves as seldom smokers, meaning that they smoked no more than 10 cigarettes a month. The participants were randomised to use e-cigarettes with nicotine for 30 minutes on the first day and without nicotine on the other day. The researchers measured blood pressure, heart rate and arterial stiffness immediately after smoking the e-cigarettes and then two and four hours later. In the first 30 minutes after smoking e-cigarettes containing nicotine, there was a significant increase in blood pressure, heart rate and arterial stiffness; no such effect was seen on heart rate and arterial stiffness in the volunteers who had smoked e-cigarettes without nicotine. "The results are preliminary, but in this study we found there was a significant increase in heart rate and blood pressure in the volunteers who were exposed to e-cigarettes containing nicotine. Arterial stiffness increased around three-fold in those who were exposed to nicotine containing e-cigarettes compared to the nicotine-free group," said lead researcher Magnus Lundback, from the Danderyd University Hospital, Karolinska Institute in Sweden. According to the researchers who presented the research at the European Respiratory Society (ERS) International Congress, the immediate increase in arterial stiffness that they saw is most likely attributed to nicotine. The increase was temporary. However, the same temporary effects on arterial stiffness have also been demonstrated following use of conventional cigarettes. "Chronic exposure to both active and passive cigarette smoking causes a permanent increase in arterial stiffness. Therefore, we speculate that chronic exposure to e-cigarettes with nicotine may cause permanent effects on arterial stiffness in the long term. As of today, there are no studies on the long-term effects on arterial stiffness following chronic e-cigarette exposure," Lundback added. Researchers are also continuing to investigate the effects of e-cigarettes on blood vessel and lung functions in humans, as well as carrying out studies in the lab of the effect of e-cigarette vapour and liquid on cell cultures.