Infections may impair cognitive ability as measured on an IQ scale, data from a large study has shown. Findings from the study are published in PLOS ONE.

Earlier research on animals have shown that the immune system can affect cognitive function, as well as more recent minor studies in humans. This nationwide register study tracked 190,000 Danes born between 1974–1994, who underwent an IQ assessment between 2006–2012. Before the IQ testing, 35% of the subjects had hospital contact with infections.

RELATED: Study on NFL Retirees Reveals Impact of Concussion History on Memory

Researchers found a link between hospitalization due to infection and impaired cognition corresponding to an IQ of 1.76 below average. Subjects with ≥5 hospital contacts with infections had an IQ score of 9.44 below average. The study demonstrates a dose-response relationship between the number of infections and the effect on cognitive ability increased with temporal proximity of the last infection and with the severity of the infection. While infections in the brain affected cognitive ability most, other types of severe infections could also impair cognitive ability.

Study data further suggests that the immune system’s response to infection, not just the infection itself, may possibly affect the brain and also a person’s cognitive ability. Previous research has shown that infections are associated with an increased risk of developing psychiatric disorders such as depression and schizophrenia.  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, added that he hopes learning more about this correlation will “help to prevent the impairment of people’s mental health and improve future treatment.”

 While the study has been adjusted for social conditions and parental educational levels, the authors do point out that heritable and environmental factors may also account for the lowered IQ scores.

For more information visit