MONDAY, April 11, 2005 (HealthDay News) -- The effects of smoking may travel through the generations, not just the umbilical cord.
New research suggests that a young child whose grandmother smoked while pregnant may have double the risk of developing childhood asthma, compared to a child whose grandmother didn't smoke during this critical period.
This study is apparently the first to demonstrate this link, said the researchers, from the University of Southern California, in Los Angeles. It appears in the April issue of the journal Chest.
The number of people in the United States with asthma has more than doubled in the last 20 years, most notably among preschool children, making the disease a significant public health burden, the researchers said.
Second-hand smoke is known to trigger asthma and contribute to children missing school days. In addition, recent evidence indicates that mothers who smoked while pregnant may contribute to their children developing asthma.
For the new study, the researchers conducted interviews with parents or guardians of 908 children, 338 of whom had had asthma during their first five years of life and 570 of whom did not have asthma. Information on maternal and household smoking histories as well as other asthma risk factors was gathered. All the participants lived in southern California.
The study relied on observation only, and did not look at any possible biological mechanisms that might cause asthma.
Children whose mothers had smoked while pregnant were 1.5 times as likely to develop asthma early in life, compared to children whose mothers did not smoke.
But surprisingly, children whose grandmothers smoked while pregnant were 2.1 times more likely to develop the respiratory condition.
If the child's grandmother smoked while pregnant but the mother did not, the child was 1.8 times more likely to develop asthma. If both the mother and grandmother smoked, the child was 2.6 times more likely to develop the disease.
The researchers can't say why this relationship may exist, but it's possible that chemicals from tobacco somehow affects a fetus's DNA. If the child is female and her eggs are damaged, that could affect her future children. Also, any damage to the fetus's mitochondria, a critical component of cell function, could be passed down through the maternal line. In either case, the DNA damage may put children and grandchildren at risk for asthma by compromising their immune function, the researchers said.
In fact, earlier research unrelated to this study had shown that women who smoke during pregnancy could be causing chromosomal abnormalities in fetal cells that may increase risks for both childhood and adult leukemia.
It's impossible to change the past, but the study findings may help people with breathing problems whose grandmothers smoked during pregnancy, experts said.
"When a child has wheezing and asthma-like symptoms before age 5, it's hard to predict if they're going to go on to have true asthma," said Dr. Jonathan Field, a specialist in pediatric allergy and asthma at New York University Medical Center in New York City. "Maybe we could use this as part of a child's history, one more thing to stack up to make a determination of whether the child will develop asthma based on family history."
The new study should also provide incentive to future grandmothers to stop smoking before they get pregnant or quit when they know they are pregnant.
There weren't enough women in the study who stopped smoking during pregnancy to assess whether quitting during pregnancy changed the odds of asthma for future generations.
A separate study, this one appearing in the May 15 issue of Cancer, found that smokers who received one or more abnormal results using spiral chest computed tomography screening were more likely to quit. The more abnormal readings a person got, the more likely they were to quit and remain smoke-free at the end of three years, the study found.
The American Lung Association can tell you more about quitting smoking during pregnancy.