A new study finds that babies whose parents smoke have five times higher levels of the nicotine marker cotinine in their blood than children of nonsmokers, Reuters reported Nov. 13.

Researcher M.P. Mailoo of the University of Leicester in Great Britain and colleagues studied cotinine levels in babies between the ages of 10 and 12 weeks. They found that having a mother who smoked was the single biggest risk factor for early nicotine exposure, and that exposure rose during the winter months, when parents were more likely to smoke indoors.

Researchers said early exposure to nicotine was especially dangerous because infants may not be able to properly excrete the drug.

The research was published in the November 2007 issue of the Archives of Disease in Childhood.