Parents' decision to make their apartment or townhome unit a smoke-free zone might not offer their children enough protection from tobacco exposure, suggests a study finding significant levels of a tobacco metabolite among children in housing complexes where residents of other units smoke.

The New York Times reported in a Dec. 13 blog that according to a study led by Dr. Jonathan P. Winickoff, associate professor of pediatrics at MassGeneral Hospital for Children, children living in apartments showed the highest blood level of the tobacco metabolite cotinine. Children in townhomes showed less exposure to cigarette smoke than did children in apartments, but more exposure than children living in detached houses. Family income did not affect the study results.

“People already understand that smoke doesn't stop at the doorway,” said Winickoff. “This study is the last link in the chain of evidence; it doesn't stop at the doorway – and we see it in the blood of kids.”

For the study, which excluded any child living with a smoker, researchers analyzed blood taken from more than 5,000 youths ages 6 to 18. A total of 56.4 percent of children living in apartments showed a high level of cotinine (at least 0.05 nanograms per milliliter of blood), compared with 47 percent of children in attached homes and 36.1 percent of children in detached homes.

Mean levels of cotinine across the study population also were highest in the apartment-dwelling group.

Several public health experts see the findings as confirming the need to ban smoking in public housing, and as possibly broadening efforts to prohibit smoking in other multi-unit housing. The U.S. Department of Housing and Urban Development (HUD) last year urged local housing authorities to institute smoke-free policies for their complexes.

Study results were published online Dec. 13 in Pediatrics.