Infections Can Lower Your IQ

In addition to causing pain and discomfort and requiring antibiotics, a Danish study revealed that infections can negatively affect cognitive ability.

Previous research had indicated that there are ties between mental illnesses such as schizophrenia and depression; however, the new study focused on finding if the same was true in healthy people. Led by Michael Eriksen Benrós, MD, PhD, the researchers from Aarhus University confirmed that constant infections can take a mental toll on patients.

“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 in a news release.

This is the largest study of its kind and included 161,696 males from Denmark born from 1974 and 1994 — the average age being 19.4. Documented in PLOS ONE, the participants’ intelligence quotient (IQ) were measured between 2006 and 2012 and it was noted that 35% had hospital exposure before the testing began.

The assessment included logical, verbal, numerical, and spatial reasoning and the average cognitive score was 100 with a standard deviation of 15. The data revealed that those who visited the hospital just once due to infection had a lower average IQ of 1.76. That number jumped to 9.44 for those who went 5 times or more.

“The associations between infections and the general cognitive ability persisted after adjusting for a wide range of possible confounders,” the study noted. “Including parental educational level, year of testing, birth order, multiple birth status, birth weight, gestational age, a parental history of infections, parental and individual history of psychiatric disorders and substance abuse.”

As what would be expected, infections in the brain had the strongest effect on cognitive ability. However, Benrós explained that any type of infection that required hospitalization made an impact as well. Now that the connection between infections and IQ has been verified, the authors suggest that future research be focused on the immune system’s role in this scenario — a factor previously proven to affect animals.

“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,” Benrós concluded.