Teens exposed to secondhand smoke have measurably thicker arteries than adolescents who are not exposed, suggesting that for children "even a little exposure to tobacco smoke may be harmful for blood vessels," according to researcher Katariina Kallio of the University of Turku in Finland.

Reuters reported March 2 that researchers studied 494 children ages 8-13, checking their blood for the nicotine marker cotinine and measuring the thickness of their aorta and carotid arteries using ultrasound. They found that the children with the highest levels of cotinine in their systems had arteries 7 percent thicker than those with the lowest cotinine levels.

"These findings suggest that children should not face exposure to tobacco smoke at all," Kallio said.

The study was published online in the journal Circulation: Cardiovascular Quality and Outcomes.