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Infection linked to lower IQ, mental illness

Kathleen Blanchard's picture
Human Brain and IQ

Results of a Danish study suggest frequent infections could lead to lower IQ. The finding is important because it suggests infection and immune response can affect memory and may contribute to mental health illness.


Researchers for the new study found infection can affect the brain by lowering IQ years after the infection is treated and cured. The finding has implications that scientists say could extend to understanding more about mental health.

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 explains: "We can see that the brain is affected by all types of infections. Therefore, it is important that more research is conducted into the mechanisms which lie behind the connection between a person's immune system and mental health."

Infection linked to lower IQ

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For this study researchers looked at data from 190,000 Danes born between 1974 and 1994. All had their IQ tested between 2006 and 2012.

IQ was 9.44 points lower than average for those who had 5 or more hospitalizations due to infection. The study found a correlation between lower IQ.

The study authors note infections and related immune responses can affect memory and IQ. Any hospitalization for infection was associated with an IQ score 1.76 points lower than average, especially infections affecting the central nervous system.

"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 said.

Benros ME, Sørensen HJ, Nielsen PR, Nordentoft M, Mortensen PB, Petersen L (2015) The Association between Infections and General Cognitive Ability in Young Men – A Nationwide Study. PLoS ONE 10(5): e0124005. doi:10.1371/journal.pone.0124005 May 15, 2015.