Both smoking and drinking cause arteries to stiffen. And if a teen smokes or drinks, it affects their arteries the same way — there is a measurable change in the elasticity of a teen's arteries. As you might expect, if a teenager both smokes and drinks, it leads to even more damage.

These adolescents haven't even reached the age of 18, yet their arteries are already on the road to old age.

There is good news, however, a European study finds. If teens stop smoking and drinking, their young arteries are able to return to normal.

The worst effects were seen in teens who were both heavy smokers and drinkers. Their arteries were almost 11 percent stiffer than those of teens who had never smoked and did not drink a lot. These adolescents haven't even reached the age of 18, yet their arteries are already on the road to old age.

Even more disturbing was that what the study defined as being a heavy smoker was pretty mild — someone who had smoked 100 cigarettes in the last five years. That could be fewer than two cigarettes a month.

Healthy arteries are flexible and elastic. They stiffen as people age. They can also narrow and become clogged, often to the point where not enough blood can flow through them. Health practitioners often use the terms atherosclerosis (narrowing and clogging) and arteriosclerosis (stiffening/hardening) to describe these two processes. Both have severe consequences for the heart and circulation, including an increased probability of heart attack and stroke.

Researchers at University College London wanted to see how the smoking and drinking habits of teens in the United Kingdom affected arterial stiffening. They looked at five years worth of information from more than 1250 teens who had participated in a study known as Children of the 90s. The data included the teens' smoking and drinking behavior at ages 13, 15 and 17. Measurements were also taken as the blood travelled through their arteries to calculate arterial stiffness.

“Injury to the blood vessels occurs very early in life as a result of smoking and drinking and the two together are even more damaging,” said lead author Marietta Charakida. “Although studies have shown teenagers are smoking less in recent years, our findings indicated approximately one in five teenagers were smoking by the age of 17. In families where parents were smokers, teenagers were more likely to smoke.”

Teens often see smoking and drinking alcohol as a normal part of adult life, as an accompanying editorial points out. Perhaps if more parents and doctors explained that they aren't, fewer teens would get started. After all, it's much easier not to start than it is to quit.

The study appears in the European Heart Journal.