Childhood asthma may be linked to grandmother's smoking

A child whose grandmother smoked while pregnant may have double the risk of developing childhood asthma, according to new research.

A study published in the April issue of CHEST, the peer-reviewed journal of the American College of Chest Physicians, suggests that the harmful effects of tobacco products can be passed through the generations, even if the damage is not visibly apparent in the second generation.

"This is the first study to show that, if a woman smokes while she is pregnant, both her children and grandchildren may be more likely to have asthma as a result," said the study's author, Frank D. Gilliland, MD, PhD, Keck School of Medicine of the University of Southern California, Los Angeles, CA. "The findings suggest that smoking could have a long-term impact on a family's health that has never before been realized."

Researchers from the Keck School of Medicine analyzed data from telephone interviews with parents or guardians of 908 children. A total of 338 of the children had asthma within their first five years of life, and 570 served as a control group. The study showed that children with mothers who smoked while pregnant were 1.5 times more likely to develop asthma early in life, and those children with grandmothers who smoked, while pregnant, were 2.1 times more likely to develop asthma. Further analysis revealed that even if a child's mother did not smoke while she was pregnant, but the child's grandmother did, the child was 1.8 times more likely to develop asthma. If both the mother and grandmother smoked while pregnant, a child was 2.6 times more likely to develop asthma.

"A potential explanation for our unexpected results is that when a pregnant woman smokes, the tobacco affects her fetus's DNA," said Dr. Gilliland. "We speculate that the damage that occurs affects the child's immune system and increases her susceptibility to asthma, which is then passed down to her children."

Researchers conjecture that when a pregnant woman smokes, biological damage is done to her fetus, and the chemicals from the tobacco can affect the child in two ways. First, if the child is female, her eggs can be affected, which puts her future children at risk. Second, damage may be done to the fetus's mitochondria, which is then transmitted through the maternal line, as well. Either effect can put a woman's children and grandchildren at an increased risk of asthma, by decreasing their immune function.

"These findings indicate that there is much more we need to know about the harmful effects of in utero exposure to tobacco products," said Paul A. Kvale, MD, FCCP, President of the American College of Chest Physicians. "They also demonstrate how important smoking cessation is for both the person smoking and their family members."