Infants with at least one parent who smokes have higher levels of a nicotine metabolite in their bodies than the children of nonsmokers, the Guardian reported June 19.

Researchers from the University of Leicester and Warwick Medical School said the study showed that smoking parents are turning their infants into passive smokers, putting them in danger of breathing problems and crib death. "Babies and children are routinely exposed to cigarette smoke by their [caregivers] in the home without the legislative protection available to adults in public places," the authors stated.

Babies whose mothers smoked had cotinine levels four times higher than children whose parents were both nonsmokers, while babies with fathers who smoked had cotinine levels twice as high.

Cotinine levels were higher among babies who shared a bed with their parents, and during the winter. "Higher cotinine levels in colder times of year may be a reflection of the other key factors which influence exposure to passive smoking, such as poorer ventilation or a greater tendency for parents to smoke indoors in winter," the authors said.

The study was published in the online edition of the journal Archives of Diseases in Childhood.