Canadian scientists have come to the conclusion that children begin to smoke not only in imitation of their parents, but also because their lungs “join” smoking at home.

They not only lead by example, but also introduce children to the taste of tobacco, increasing the likelihood that they will become chain smokers.

A group at the Montreal Chest Institute, led by Margaret Becklake , watched about 200 children grow up. When they were about nine years old, scientists measured the concentration of cotinine in their saliva, reports NEWSru.com.

Cotinine is the metabolic by-product of nicotine, which causes tobacco addiction. When tobacco smoke is inhaled, nicotine is converted to cotinine , and its concentration in blood and saliva can be measured.

Concentration of cotinine in children was different, scientists write in the Canadian Medical Association Journal. Only one child showed levels of cotinine at this stage , suggestive of an existing smoker.

Scientists conducted a second examination when the children were about 13 years old. By this point, 80% of them were high school students, and 44% were smokers.

Scientists have found that the level of cotinine , determined in the first stage, is a fairly accurate indicator of whether children will smoke by the second stage. This is especially true for those who started smoking at an early age.

Those whose cotinine levels were high at age nine were twice as likely to start smoking before puberty. For those who had already entered puberty, cotinine did not matter as much, increasing the risk by only 20%.

Thus, parents smoking in front of their children do more harm than they think, the scientists conclude, emphasizing that the number of participants was small and the findings should be interpreted with caution, but the results are nonetheless impressive.

Meanwhile, scientists have not found a relationship between the number of smokers in the family and the chances of a child to smoke in adolescence. The relationship between cotinine levels and subsequent smoking persists even after adjusting for the socioeconomic status of parents, the number of smokers in the family, and the number of cigarettes smoked at home.

“ Firstly, the children of smoking parents imitate them, learn from their example. It is not surprising that the concentration of cotinine in the blood and saliva of these children is higher than normal, because the parents smoke at home ,” said Ian Wilmore from the Anti- Smoking Organization.

“ Secondly, there may be disturbing evidence that nicotine produced in saliva from passive smoking can lead to physical dependence, and the study suggests such a conclusion ,” he added.

“ It is important to draw the attention of parents to the fact that when they smoke at home, they harm the health of their children, and that if they smoke, the likelihood that children will also smoke increases ,” the scientist states.

In addition, scientists have found a weak relationship between lung capacity and the tendency to smoke. “We believe that lung size increases the amount of smoke inhaled, maximizes the impact of secondhand smoke on children, and encourages smoking in adolescence,” they write.

If the link is confirmed, it would provide a simple explanation of how smoking is passed down from generation to generation and could form the basis of anti-smoking campaigns, write Canadian physicians Nicholas Antonisen and Robert Murray in a commentary in the same journal.