MONDAY, Dec. 13 (HealthDay News) -- Children who live in smoke-free apartments but have neighbors who light up suffer from exposure to smoke that seeps through walls or shared ventilation systems, new research shows.

Compared to kids who live in detached homes, apartment-dwelling children have 45 percent more cotinine, a marker of tobacco exposure, in their blood, according to a study published in the January issue of Pediatrics.

Although this study didn't look at whether the health of the children was compromised, previous studies have shown physiologic changes, including cognitive disruption, with increased levels of cotinine, even at the lowest levels of exposure, said study author Dr. Karen Wilson.

"We think that this research supports the efforts of people who have already been moving towards [banning smoking in multi-unit housing] in their own communities," added Wilson, an assistant professor of pediatrics at Golisano Children's Hospital at the University of Rochester Medical Center in New York.

Vince Willmore, vice president of communications at the Campaign for Tobacco-Free Kids, agreed. "This study demonstrates the importance of implementing smoke-free policies in multi-unit housing and of parents adopting smoke-free policies in all homes," Willmore said. Since smoke doesn't stay in one place, Willmore said only comprehensive smoke-free policies provide effective protection.

The authors analyzed data from a national survey of 5,002 children between 6 and 18 years old who lived in nonsmoking homes. The children lived in detached houses, attached homes and apartments, which allowed the researchers to see if cotinine levels varied by types of housing.

About three-quarters of children living in any kind of housing had been exposed to secondhand smoke, but apartment dwellers had 45 percent more cotinine in their blood than residents of detached houses. For white apartment residents, the difference was even more startling: a 212 percent increase vs. 46 percent in blacks and no increase in other races or ethnicities.

But a major limitation of the study is that the authors couldn't separate other potential sources of exposure, such as family members who only smoked outside but might carry particles indoors on their clothes. Nor did it take into account day-care centers or other forms of child care that might contribute to smoke exposure.

Even so, Willmore said, "It's critical that we take additional action to protect our children from secondhand smoke," especially in light of a recent report from the U.S. Centers for Disease Control and Prevention stating that more than half of children aged 3-11 are exposed to secondhand smoke.

"Some municipalities, especially in California and Washington, have started moving towards [restricting smoking in multi-unit housing], and in New York City some private apartment buildings and condominium complexes have banned smoking," said Wilson.

Noting that some consider a smoking ban in apartments an infringement upon personal rights and privacy, the authors say the civil liberties argument only holds if the smoke has no impact on one's neighbors.

"We also feel very strongly that if we're going to be putting restrictions on smoking in people's homes . . . we need to be sure we have the resources in place for smokers to either cut down or smoke in other places," said Wilson.

But such initiatives have already angered advocates of smokers' rights and are likely to do so again.

A second study in the same issue of Pediatrics found that as smoke-free laws get tougher, kids' asthma symptoms, though not asthma rates, are declining.

Researchers from the Harvard School of Public Health examined U.S. health data from 1999 to 2006, and found a 33 percent decline in symptoms, including persistent wheeze and chronic night cough, among kids who weren't exposed to smoke.

Prior research from the same group had found that tougher laws were also linked with lower cotinine levels in children and adolescents, down about 60 percent between 2003 and 2006 in children living in smoke-free homes.

According to the study authors, 73 percent of U.S. residents are now covered by smoke-free laws.

More information

The U.S. Environmental Protection Agency has more on how to protect yourself and your children from secondhand smoke.