Cigarettes: Exposure to tobacco smoke in childhood could be related to cancer later in life

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A cancer-causing chemical has been found in babies whose parents smoke around them, according to new research from the US.

The study of 144 infants between three and 12 months old found that almost half (47%) had NNAL - a compound associated with tobacco - in their urine.

Previous research has looked at exposure to smoking before birth and during childhood, but this is the first time such young babies have been tested.

"These findings support the concept that persistent exposure to environmental tobacco smoke in childhood could be related to cancer later in life," lead author Stephen Hecht, from the University of Minnesota, said.

NNAL has been shown to cause cancer of the lung, pancreas, liver and nasal cavities in laboratory animals, although a direct link to human malignancies has not been definitively proven.

The compound is produced in the human body as it processes NNK, a carcinogenic chemical specific to tobacco.

"The take home message is, 'Don't smoke around your kids'," Dr Hecht said.

He added: "The level of NNAL detected in the urine of these infants was higher than in most other field studies of environmental tobacco smoke in children and adults.

"NNAL is an accepted biomarker for uptake of the tobacco-specific carcinogen NNK.

"You don't find NNAL in urine except in people who are exposed to tobacco smoke, whether they are adults, children, or infants."

The study found that babies had detectable levels of NNAL when family members smoked an average of 76 cigarettes per week, in their home or car while the babies were present.

In the cases where the levels of NNAL were undetectable, the average number of cigarettes smoked by family members was 27.

The research was published in the journal Cancer Epidemiology, Biomarkers and Prevention.