CHILDREN become smokers not only by following their parents’ example but also by having their lungs “primed” by smoke in the home, according to a Canadian study.

The research suggests that parents do more harm than they realise when they smoke in front of their children.

Not only do they set an example, but they also give their children a taste for tobacco that increases their chances of becoming smokers.

A team from Montreal Chest Institute led by Margaret Becklake followed nearly 200 children as they grew up. When they were about 9 years old the team measured levels of cotinine in their saliva.

Cotinine is the metabolic by-product of nicotine, which is the addictive element of tobacco smoke. When smoke is inhaled the nicotine is turned into cotinine and can be measured in the blood or the saliva.

The team reports in the Canadian Medical Association Journal that cotinine levels varied in the children. Only one child at the earliest stage showed cotinine levels that suggested that he or she was already a smoker.

The team re-examined the children when they were about 13. By that time, 80 per cent had entered high school and 44 per cent had become smokers.

The team found that saliva cotinine levels measured at the first stage were a good predictor of whether the children would become smokers by the time of the second — particularly among those who took up smoking very early.

Among those who had not reached puberty, the chances of becoming a smoker were doubled by high cotinine levels at the age of 9. Among those who were post-puberty, many more of whom had become smokers, the contribution of cotinine levels was smaller, adding 20 per cent to the risk.

The team points out that the numbers involved were small, and the conclusions must be interpreted with caution, but the results are nonetheless striking. The study, however, showed no link between the numbers of smokers in the home and the chance of becoming a teenage smoker. The link between cotinine levels and subsequent smoking among the teenagers still held true after adjustment for socioeconomic level of the parents, crowding in the home, the total number of smokers in the home and the total number of cigarettes smoked there.

The team also found a weak link between lung capacity and the tendency to take up smoking. They conclude: “We suggest that lung size [or some associated characteristic] increases the uptake of environmental tobacco smoke, maximises the influence of passive smoking in childhood, and induces smoking in adolescence.”

In a commentary in the same journal, two Canadian doctors, Nicholas Anthonisen and Robert Murray of the University of Manitoba, said that if the link is confirmed it will provide a simple explanation of how smoking may be passed from one generation to the next, and will be useful in targeting anti-smoking campaigns.

Responding to the study, Ian Willmore of Action on Smoking and Health, said: “First, the children of parents who smoke are more likely to follow this behaviour, learning by example. It is likely such children will have above average levels of cotinine in the blood and saliva because their parents may smoke around the home.

“Secondly, it would be extremely disturbing if evidence shows that nicotine in the saliva acquired through inhaling second-hand smoke may lead to physical addiction, which is what this study seems to be suggesting. More work would be needed to show this.

“The most effective policy instrument now available to the Government to cut adult rates is of course legislation to end smoking in all workplaces and enclosed public places, which could cut prevalence rates by up to 4 per cent.

“But it is also important to draw to parents’ attention that they may damage their children’s health if they smoke at home, and that their children may be more likely to start smoking if they themselves are smokers.”

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