May 19 (HealthDay News) -- Smoking while pregnant "biologically primes" the unborn child to become a regular smoker as a teen and young adult, according to a theory put forth by University of Arizona researchers.
"Somehow smoke is changing the brain chemistry," said the lead researcher, Dr. Roni Grad, an associate professor of clinical pediatrics at the university.
"If you are exposed to smoking prenatally or in the early years of life, you are much more likely to be a chronic smoker at the age of 22," Grad said.
In fact, these children are four times more likely to become regular smokers, according to the research, which was to be presented May 19 at the American Thoracic Society's international conference in San Diego.
For the study, Grad's team used data from the Tucson Children's Respiratory Study to see whether a mother's smoking during pregnancy and during her child's early years affected whether the child smoked later on.
The researchers assessed maternal smoking during pregnancy and when infants were 1.5 months and 1.5 years old and again when the children were 6, 9 and 11 years old. They then looked at the children's smoking behavior when they were ages 16 and 22.
They found that women who smoked during pregnancy and during their children's early years were more likely to have kids who smoked at age 22. This proved true whether the mother smoked or did not smoke during the child's school years.
In addition, the children of mothers who smoked during pregnancy and their early years were less likely to quit smoking than were the offspring of mothers who never smoked or who started smoking when their children were school-age.
The impact of early maternal smoking was not affected by whether the children's fathers smoked or by peer pressure during adolescence, the study found.
"Nobody should smoke," Grad said. "I would definitely discourage any mother from smoking around her child. If children have been exposed in early life to smoke, I would really go the extra mile to try to keep them from experimenting, because they may be at higher risk of becoming nicotine dependent very quickly."
Dr. Norman H. Edelman, a scientific consultant to the American Lung Association, said that the research provides another reason for women to stop smoking before becoming pregnant.
"We know that smoking during pregnancy confers many health risks upon the fetus, including premature birth and increased risk for asthma," Edelman said. "Now we see a new risk -- increased rates of smoking during subsequent early adulthood."
Edelman said that the researchers seem to favor a biologic explanation, such as an alteration of brain neurochemistry during pregnancy. "However, the study does not include enough information to rule out social factors, such as increased smoking of others in the household even though the mother stops after childbirth."
"When you decide to become pregnant, there are certain steps to take to optimize the health of the hoped-for child, such as taking folic acid and weight reduction for the very overweight," Edelman said. "Now, even more forcefully, we add stop smoking -- and get others in the household to do so as well."
Danny McGoldrick, vice president for research at the Campaign for Tobacco-Free Kids, agreed that the study highlights the importance of not smoking during pregnancy.
"We already know how bad smoking during pregnancy is for the fetus and the health of the child," he said. "This new research shows that smoking during pregnancy also makes the child more likely to become a smoker as an adult -- even if the mother quits smoking when the child is young."
"Aside from protecting their own health, this is one more reason that female smokers who are pregnant or considering becoming pregnant should try to quit," McGoldrick said.
Another study on the effects of smoking, also scheduled to be presented May 19 at the conference, found that children exposed to smoke may be more likely to develop emphysema later in life.
The researchers explained that smoke can damage young children's lungs, creating what's known as "emphysematous holes" in the lung. The holes begin as small areas of damage or impaired development but can lead to breathing problems later in life, even among nonsmokers, they said.
"The take-home message from our analysis is that exposure to tobacco smoke during childhood may be associated with detectable differences in lung structure, and perhaps early emphysema, later in life among people who do not themselves smoke," Gina Lovasi, a Health and Society Scholar at Columbia University, said in a prepared statement.
SOURCES: Roni Grad, M.D., associate professor, clinical pediatrics, University of Arizona College of Medicine, Tucson, Ariz.; Danny McGoldrick, vice president, research, Campaign for Tobacco-Free Kids, Washington, D.C.; Norman H. Edelman, M.D., scientific consultant, American Lung Association; May 16, 2009, presentation, American Thoracic Society's 105th International Conference, San Diego