TUESDAY, Jan. 15, 2008 (HealthDay News) -- Children born to mothers who have persistent depression or anxiety have an increased risk of developing asthma, new research suggests.
Canadian researchers report a 25 percent increase in the odds of asthma for children who are exposed to maternal distress from birth to age 7. No such association was found for short-lasting maternal distress, such as postpartum depression.
"Asthma is a multi-factorial disease, and we've identified one possible factor that might be associated with its development," said study author Anita Kozyrskyj, an associate professor in the faculty of pharmacy at the University of Manitoba in Winnipeg, Canada. "I think the good thing is that this is a risk factor that can be prevented."
The findings are published in the second January issue of the American Journal of Respiratory and Critical Care Medicine.
About 20 million Americans, including 9 million children, have asthma, according to the American Academy of Allergy, Asthma & Immunology. The exact cause of asthma remains unknown, but researchers have found many factors that can contribute to the development of the disease, such as a family history, exposure to secondhand smoke, and other environmental triggers.
Because the rise in the incidence of asthma seemed to parallel an increase in the amount of chronic stress experienced by women in general, and because other research suggested a possible link between asthma and maternal distress, Kozyrskyj and her colleagues reviewed the medical records of almost 14,000 children in Manitoba, from birth to age 7.
Asthma status was defined by having had at least two doctor visits for asthma, one asthma hospitalization or two or more prescriptions for asthma medication. Maternal distress was defined as having a doctor visit, hospitalization or prescription for depression or anxiety during the child's first year of life and beyond.
Almost one in five children included in this study was exposed to maternal distress during their first year of life, according to the study. The prevalence of asthma for the whole study population was 6.6 percent.
After adjusting the data for certain known risk factors, such as a maternal history of asthma, living in an urban area, antibiotic use and more, the researchers found a 25 percent higher risk of asthma in children whose mothers had longstanding depression or anxiety.
Interestingly, the researchers also noted that persistent maternal distress was associated with a 44 percent greater likelihood of childhood asthma in high-income households compared to those in low-income households.
Kozyrskyj said the researchers "don't completely understand this association," and can only speculate as to how maternal distress might increase the risk of asthma. Some possible theories are that mothers who are depressed or anxious may smoke more, breast-feed less, and may not pay as much attention to their offspring, any of which could contribute to the development of asthma.
Others aren't so sure about the importance of maternal distress in asthma.
"There may be something to this. I wouldn't dismiss it, but I wouldn't say this is a cause of asthma. An association doesn't mean cause and effect. This is just one more aspect of a child's environment that needs to be looked at," said Dr. Jennifer Appleyard, section chief of allergy and immunology at St. John Hospital and Medical Center in Detroit.
"There are so many variables that this really needs to be looked at in a much more controlled study," she said, adding that it would be interesting to also include the father and any other primary caregivers in any future analysis.
To learn more about depression, visit the National Institute of Mental Health.