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Study: Infections Can Affect IQ

A Danish study shows that infections can impair one’s cognitive ability as measured on an IQ scale. The largest of its kind to date, the study indicates a clear correlation between infection levels and impaired cognition.

“Our research shows a correlation between hospitalization due to infection and impaired cognition corresponding to an IQ score of 1.76 lower than the average,” explains Michael Eriksen Benrós, MD, PhD, who is affiliated with the National Centre for Register-Based Research at Aarhus BSS and the Mental Health Centre Copenhagen, University of Copenhagen. “People with five or more hospital contacts with infections had an IQ score of 9.44 lower than the average. The study thus shows a clear dose-response relationship between the number of infections, and the effect on cognitive ability increased with the temporal proximity of the last infection and with the severity of the infection.

“Infections in the brain affected the cognitive ability the most, but many other types of infections severe enough to require hospitalization can also impair a patient’s cognitive ability. Moreover, it seems that the immune system itself can affect the brain to such an extent that the person’s cognitive ability measured by an IQ test will also be impaired many years after the infection has been cured.”

Benrós has conducted the research in collaboration with researchers from the University of Copenhagen and Aarhus University.

The study uses a nationwide register to track 190,000 Danes born between 1974 and 1994, who had their IQ assessed between 2006 and 2012. Out of those, 35 percent of these individuals had a hospital contact with infections before the IQ testing was conducted.

“Infections can affect the brain directly, but also through peripheral inflammation, which affects the brain and our mental capacity,” says Benrós in explaining the connection. “Infections have previously been associated with both depression and schizophrenia, and it has also been proven to affect the cognitive ability of patients suffering from dementia. This is the first major study to suggest that infections can also affect the brain and the cognitive ability in healthy individuals.

“We can see that the brain is affected by all types of infections,” he continues. “Therefore, it is important that more research is conducted into the mechanisms that lie behind the connection between a person’s immune system and mental health,” he continues. Learning more about this connection could help to prevent the impairment of people’s mental health and improve future treatment, Benrós notes.