January 15, 2010

Study Finds No Link Between Flu And Schizophrenia

A new study has found no link in the theory that the flu pandemic of 1957 caused a risk for schizophrenia.

Researchers performed an analysis of studies from Europe, Australia, Japan and the U.S., leading them to find no evidence of a higher-than-normal risk of schizophrenia among people born in the nine months after the 1957 flu pandemic. The research was reported in the Schizophrenia Bulletin.

The findings conflict with earlier studies linking the same pandemic to a heightened schizophrenia rate.

Despite the exact causes of schizophrenia being unclear, it's believed to be caused by a disorder of disrupted brain development.  Researchers have long speculated that schizophrenia comes from a combination of genetic susceptibility and environmental factors.

One of the environmental factors suspected is fetal exposure to a mother's infection during pregnancy, with the influenza virus being one of the causes.

A Finnish study reported in 1988 that there was an increased rate of schizophrenia among those who were in the womb during the 1957 Asian flu pandemic, which took the lives of about 2 million people around the globe.

Studies have since then discovered conflicting results as to whether prenatal flu exposure might contribute to schizophrenia.  However, similar studies that used mothers' blood sample to measure flu exposure during pregnancy have helped support the theory.

In one theory, it is thought that inflammatory substances released in the mothers' blood in response to the infection may cross the placenta and affect fetal brain development, causing the child to be more vulnerable to developing schizophrenia later in life.

However, the researchers, led by Dr. Jean-Paul Selten of the University Medical Center Utrecht in the Netherlands, reported that the latest findings "do not support this hypothesis." 

The findings were based on 11 international studies that compared rates of schizophrenia among people who were in the womb during the Asian flu pandemic with people that were born within a few years before and after the outbreak.

Researchers also looked at two studies that included women who were pregnant and had reported having the flu during the pandemic.

Selten's team did not find an increased schizophrenia risk among people that were in their mothers' womb at the time of the pandemic.

The original Finnish study used an "inappropriate statistical method" to arrive at its conclusions, according to the researchers.  They also said that their re-analysis of the data showed no increased risk of schizophrenia.

"We conclude that the evidence to support the maternal influenza hypothesis is insufficient," the researchers write.


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