Environmental tobacco smoke linked to behavior problems.

A study conducted by the Cincinnati Children's Hospital Medical Center shows that exposure to environmental tobacco smoke, even at extremely low levels, is associated with behavior problems in children and preteens.

Dr. Kimberly Yolton, a researcher at the Cincinnati Children's Environmental Health Center and the study's main author, examined 225 children and preteens who were exposed to at least five cigarettes a day. On average, the children were exposed to approximately 14 cigarettes a day. The study considered only children who had asthma; the children were enrolled in an asthma intervention study, and Yolton included additional measures to assess their behaviors. But she thinks the findings most likely could be extrapolated to include children without asthma who "act out" or experience depression and anxiety.

To measure exposure to environmental tobacco smoke, Yolton measured levels of cotinine in the blood. Cotinine is a substance produced when nicotine is broken down by the body, and it can be measured in blood, urine, saliva, and hair. It is considered the best available marker of exposure to environmental tobacco smoke.

Yolton found a relationship between cotinine levels and the following patterns: increases in acting out; increases in holding things in, often manifested by anxiety and depression; increases in behavior problems as rated by parents and behavior and school problems as rated by teachers; and decreases in the ability to adapt to behavior problems.

"The greater the exposure to tobacco smoke, the greater the problems these children had," says Yolton. "Behavior problems in children have increased from 7 to 18 percent over the last 20 years for reasons that are poorly understood. Exposure to environmental tobacco smoke is increasingly recognized as a risk factor for child behavior problems."

In the United States, about 25 percent of children are exposed to environmental tobacco smoke in their homes; more than 50 percent of children have detectable levels of cotinine in their blood, according to Yolton.

Previous studies have found links between tobacco smoke and birth weight, number of infections, and other health problems, including asthma exacerbations. In a groundbreaking study in 2002, Yolton found that exposure to environmental tobacco smoke, even at extremely low levels, is associated in children and adolescents with decreases in certain cognitive skills, including reading, math, logic, and reasoning.