TUESDAY, June 19 (HealthDay News) -- In homes where at least one parent smokes, infants have 5.5 times higher levels of a nicotine toxin called cotinine in their urine than infants of nonsmokers, a British study finds.

Cotinine is created as the body tries to get rid of the nicotine in inhaled smoke.

The study of 104 12-week-old infants (71 with at least one parent who smoked and 33 with nonsmoking parents) also found that having a mother who smoked quadrupled urine cotinine levels. Having a father who smoked doubled cotinine levels in an infant's urine, the researchers found.

Sleeping with parents and lower-temperature rooms were also associated with increased cotinine levels in infants, said the study by researchers at the University of Leicester Medical School and Warwick University.

"Babies affected by smoke tend to come from poorer homes, which may have smaller rooms and inadequate heating," the study authors wrote. "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 researchers also noted that sleeping with a parent is a known risk factor for sudden infant death syndrome (SIDS). They suggest that one reason for this could be an infant's proximity to parents' clothing or other objects contaminated with smoke particles.

The findings were published online Tuesday ahead of print in the journal Archives of Disease in Childhood.

More information

The American Academy of Otolaryngology -- Head and Neck Surgery has more about children and secondhand smoke.