Children as young as seven affected by passive smoking

A new study published today shows that children as young as seven who are exposed to second-hand cigarette smoke from their mother have elevated levels of cotinine, a by-product of nicotine, in their blood.

Exposure to tobacco smoke, even through second-hand or 'passive' smoking, has been linked to increased risk of heart disease, lung cancer and other respiratory diseases. The researchers say the study provides important new evidence of the need to reduce smoking in private homes and cars.

The study looked at cotinine levels in children who had taken part in the Children of the 90s study at the University of Bristol, including more than 3,000 children aged 7 and 2,000 children aged 15. The researchers found that the cotinine levels of children at both ages were strongly related to whether the mother smoked, and how heavily, indicating clear evidence of passive smoking.

Strikingly, the cotinine levels of non-smoking 15-year-olds were five times higher if their mother smoked ten or more cigarettes a day, compared with the children of non-smoking mothers. For 7-year-olds, they were four times higher. These levels of passive smoking exposure at age seven and 15 are comparable to the levels of exposure seen at age 15 in teenagers who smoke occasionally (less than once a week).

Speaking about the findings, the lead author, Alex Stiby, said: "We have found that the children of mothers who smoke have elevated cotinine levels, indicating clear evidence of passive smoking exposure. This provides a strong public health message about the risks to children if there are adults smoking in the home. Our research shows that the risks apply to older children just as much as to younger ones."

Professor Marcus Munafò, the senior academic on the paper, said: "At the age of seven, it is highly unlikely that children have started smoking, so the presence of cotinine in their blood at this age provides clear and conclusive evidence of the risks to young children from adults smoking at home."

By quantifying the magnitude of passive smoking that a child is exposed to by having a heavy smoker in the home, it is hoped the study's findings will encourage mothers to stop smoking altogether or to introduce smoking restrictions in the home to reduce exposure.

'Children of the 90s' has been studying children born in the early 1990s in the former county of Avon, England, and their parents for more than 21 years with core funding from the Wellcome Trust, the Medical Research Council and the University of Bristol. Detailed records are kept of everyday characteristics (e.g. diet, lifestyle, socioeconomic status, parent-child contact and so on), as well as tens of thousands of samples of urine, blood and DNA. The findings from this study were made possible by a retrospective analysis to measure levels of cotinine in stored blood samples.

The findings are published today in the journal 'Nicotine and Tobacco Research'.