That's the startling conclusion of new research that found children who are exposed to secondhand -- or "environmental" -- smoke scored slightly lower on standardized tests on reading, math and reasoning. A second study on the hazards to children from exposure to smoking says babies whose mothers had smoked while pregnant had abnormal heart rhythms.
Both studies are being presented today at the annual meeting of the Pediatric Academic Societies in Baltimore.
"Parents need to be more aware of when and where their children are being exposed to environmental tobacco smoke, and to try to protect them from it," says the first study's author, Kimberly Yolton, a research associate at the Children's Environmental Health Center at Cincinnati's Children's Hospital Medical Center.
Yolton and her colleagues studied data on 4,399 children involved in a national study. The children were between the ages of 6 and 16, and from across the United States. The boys and girls were also of different races and socioeconomic backgrounds.
All the children took standardized tests to measure reading, math, reasoning and memory skills. Blood samples were drawn to measure the amount of cotinine in the children's blood.
Cotinine is a substance created by the body as it breaks down nicotine. The average amount of cotinine was 0.7 nanograms per milliliter (ng/ml) of blood, and more than 80 percent of the children had an amount less than 1 ng/ml, Yolton says.
While Yolton couldn't estimate how much exposure to smoke would produce such cotinine levels, she says an average smoker produces about 15 ng/ml when he or she smokes just one cigarette. It's difficult to say how much cotinine would be produced in a child if someone smoked a single cigarette next to one because secondhand smoke is metabolized differently, and there are many variables that could affect the levels, such as a window being open, she says.
The researchers then looked to see how varying levels of cotinine affected test scores. They saw slight declines in test scores when cotinine levels were as low as 0.5 ng/ml. The more cotinine, the lower the scores.
"Children with more exposure were performing lower than those with less exposure," Yolton says.
On reading tests, Yolton says, the researchers found a one-point decrease in test scores for each 1 ng/ml increase in cotinine. In math, it was about a 0.75-point decrease for each additional unit of cotinine. Both of these tests were based on a scoring scale of 100.
On the reasoning tests, there was a 0.23-point decline in scores for each 1 ng/ml increase in cotinine. However, these tests were based on a scoring system of 10 points, so Yolton says the difference was more significant.
There was no apparent affect on the memory test.
"It's a very small effect they're seeing," says Dr. Peter Stavinoha, a neuropsychologist at Children's Medical Center of Dallas. "But if we keep identifying factors that account for a point here and a point there, eventually you do come up with a significant difference. It's important to take away any obstacle to children's development. If we can remove an environmental factor, we should."
In the second study, researchers from Carolinas Medical Center in Charlotte, N.C., found babies who had been exposed to smoke in the womb had higher rates of abnormal heart rhythms than babies who weren't exposed.
The researchers studied the responses of 46 newborns; 22 had mothers who'd smoked during pregnancy.
Babies born to women who smoked less than half-a-pack a day had slower heart rhythms and showed "less arousal." Babies whose mothers smoked more than a pack a day had higher-than-normal heart rates, which suggests the babies were suffering from nicotine withdrawal, the researchers say.