A new study at the University of Manitoba, Canada, has found that kids whose mothers suffer prolonged depression or anxiety have a higher rate of asthma than their peers, independent of other risk factors for the increasingly common respiratory condition.
The study, led by Anita Kozyrskyj, Ph.D., Associate Professor in the Faculty of Pharmacy at the University of Manitoba, Canada, appear in the second issue for January of the American Journal or Respiratory and Critical Care Medicine.
"Evidence is emerging that exposure to maternal distress in early life plays a causal role in the development of childhood asthma. In a cohort of children born in 1995, we found that maternal distress which persists beyond the postpartum period is associated with an increased risk of asthma at school-age," Dr. Kozyrskyj said.
For the study, Dr. Kozyrskyj's team analysed the medical records of nearly 14,000 children born in Manitoba in 1995 who were continuously registered with Manitoba Health Services until 2003.
They checked to see whether the children had asthma at age seven by analysing records of doctor visits, hospitalisations and medications in the year of their seventh birthday.
They crosschecked this with the mother's medical records, including doctor visits, hospitalisations and medication for depression and anxiety.
And they ranked maternal distress by the duration of treatment: no distress, postpartum distress only, short-term distress and long-term distress.
"Unlike existing studies that have measured maternal stress during the first few years only, the longitudinal nature of our health care study enabled us to characterize maternal distress over time to identify whether it continued," Dr. Kozyrskyj said.
Even after taking into account known risk factors of male gender, maternal asthma, urban location and total health care visits, long-term maternal stress was linked to an increase of nearly a third in the prevalence childhood asthma.
The risk appeared to intensify for children in high-income households or who had more than one sibling.
While the reason these children are at higher risk is not clear, Kozyrskyj said it may be that mothers who are distressed are less likely to breast-feed and more likely to smoke.
However, research has also suggested that depressed mothers are also less likely to interact with their infants.
"Our maternal distress measure captured women who sought health care for their depression and anxiety, and thus, our findings may be limited to more severe depression and anxiety," Dr. Kozyrskyj said.
"We plan to further explore the role of postpartum distress by doing a similar study which will link health care records with public health nurse assessments of depression and anxiety from a provincial postnatal screening program. This will enable us to assess the effects of less severe depression and anxiety during the postpartum period," she added.
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