Children born after being exposed to the flu during pregnancy may have a nearly four-fold higher risk of later developing bipolar disorder, according to a small new study.
The senior researcher said the results can't prove that a mother's bout of flu while pregnant causes her child to develop the mental disorder, but the association does suggest that some cases might be prevented.
"The idea is that if influenza is playing a causal role - and we can't say that from one study - there is a vaccine," Dr. Alan Brown, a professor of psychiatry and epidemiology at Columbia University in New York, told Reuters Health.
"It's affordable and also I would argue that there are other things that pregnant women could do. For example, hand washing and staying away from people with the flu," Brown said.
Previous studies had already established a link between a mother's flu infection while pregnant and her child's increased risk of developing schizophrenia, a severe mental disorder that often comes with hallucinations, delusions and paranoia.
Bipolar disorder shares some traits of schizophrenia, but also differs because it includes alternate cycles of mania and depression - although one type of bipolar diagnosis involves mania alone.
Past research into the link between people's risk of bipolar disorder and their mother's flu has produced mixed results, Brown and his colleagues write in JAMA Psychiatry.
For the new study, Brown's group looked for a connection between flu exposure and children's bipolar diagnoses in data from a study that involved soon-to-be mothers living in Alameda County, California, between 1959 and 1966.
Using the mothers' medical records and follow up information about their children, the researchers had information on 92 kids who were exposed to the flu while in the womb, and on 722 who were not.
Of the children exposed to the flu, about 9 percent were later diagnosed with bipolar disorder. That compared to about 3 percent of the kids who were not exposed.
"What we found is that (schizophrenia and bipolar disorder) share at least this in common. Maternal influenza is related to bipolar disorder," Brown said. He added, however, that they did not see an association between bipolar disorder and a mother's common cold or other upper respiratory infections.
And until more studies are done, Brown said he and his colleagues can only guess at what is behind the link between flu and bipolar disorder.
"We think there is an inflammation going on in the fetus due to this infection and it can alter key aspects of brain development and function," Brown said.
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