Smoking even one cigarette daily increases the stiffness of the arteries in young adults, aged between 18 and 30 years, by nearly 25 per cent. Stiff arteries increase resistance in blood vessels, making the heart work harder. This increases the risk of heart diseases including an attack.As part of the study, researchers compared arterial stiffness of young smokers, who smoke five to six cigarettes per day, to non-smokers using 'Applanation tonometry' method.