05/26/2015 12:50 pm ET | Updated May 27, 2015

Severe Infections In Childhood Linked To Lower IQ

Shutterstock / TheTun

By: Julia Calderone
Published: May 22, 2015 11:16am ET on LiveScience.

People who have had an infection that made them so sick they had to be hospitalized may have IQs that are slightly lower than average, a new study suggests.

Researchers from the University of Copenhagen and Aarhus University in Denmark examined the hospital records of 190,000 Danish men born between 1974 and 1994. All the men took IQ tests at age 19, as part of the process of signing up for Denmark's mandatory draft. The tests were designed to assess their logical, verbal, numerical and spatial reasoning.

After adjusting for factors known to track with people's IQ scores, such as social conditions and the education levels of their parents, the researchers found that the average IQ score of the men who had been hospitalized for an infection before they took the IQ test — about 35 percent of the study cohort — were 1.76 points below the average of the men in the study who had not been hospitalized for an 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," study author Dr. Michael Eriksen Benrós, a researcher at the National Centre for Register-Based Research, said in a statement.

Moreover, the more times a person was hospitalized, the lower his IQ, researchers found. Those with five or more hospitalizations for infection had an average IQ that was 9.44 points below the average of those who were not hospitalized. [10 Ways to Keep Your Mind Sharp]

Hospitalization for bacterial infections tended to lower cognitive scores by about 1.55 points, and hospitalizations for viral infections lowered them by about 1.34 points, the researchers said.

The study shows that there is a strong relationship between the number and severity of infections a person has and that person's cognitive ability, according to the authors. The infections seen in the study included those of the stomach, urinary tract and skin, as well as some sexually transmitted infections such as herpes.

Infections have previously been linked to increased risks of depression and schizophrenia, and may even worsen the cognitive declines associated with dementia, according to the study. But this is the first study to suggest that infection may harm the brain and cognition of healthy people.

Although it's not clear exactly how infections may affect a person's IQ, the study authors said it's possible that the immune system, and not the infection itself, affects the brain. When the body launches an attack against a foreign invader, it activates an immune response that can lead to inflammation. The brain is generally protected from this attack, but perhaps sometimes the brain can be affected.

"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," said Benrós in a statement.

It could also be that inflammation elsewhere in the body negatively affects the brain, the researchers suggest. Animal experiments and some recent, small studies on people have indicated that the immune system may contribute to cognitive decline. However, more research is needed to determine whether genetic or environmental factors may play a role, the researchers said.

The study authors said they hope that their results will spark more research into the immune system's possible role in the development of psychiatric disorders. It is unclear whether infection-related inflammation may actually cause mental disorders to develop, or whether other factors may be involved, such as a genetic predisposition toward both infection and a lowered cognitive ability, the researchers said.

The study was published May 13 in the journal PLOS ONE.

Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.

Copyright 2015 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.


  • 1 Ebola is highly infectious and even being in the same room as someone with the disease can put you at risk
    Not as far as we know. Ebola isn't contagious until symptoms begin, and it spreads through direct contact with the bodily fluids of patients. It is not, from what we know of the science so far, an airborne virus. So contact with the patient's sweat, blood, vomit, feces or semen could cause infection, and the body remains infectious after death. Much of the spread in west Africa has been attributed to the initial distrust of medical staff, leaving many to be treated at home by loved ones, poorly equipped medics catching the disease from patients, and the traditional burial rites involving manually washing of the dead body. From what we know already, you can't catch it from the air, you can't catch it from food, you can't catch it from water.
  • 2 You need to be worried if someone is sneezing or coughing hard
    Apart from the fact that sneezing and coughing aren't generally thought to be symptoms of Ebola, the disease is not airborne, so unless someone coughed their phlegm directly into your mouth, you wouldn't catch the disease. Though medical staff will take every precaution to avoid coming into contact with the body of an infected person at all costs, with stringent hygiene there should be a way to contain the virus if it reaches the UK.
  • 3 Cancelling all flights from west Africa would stop the spread of Ebola
    This actually has pretty serious implications. British Airways suspended its four-times-weekly flights to Liberia and Sierra Leone until the end of March, the only direct flight to the region from the UK. In practice, anyone can just change planes somewhere else and get to Britain from Europe, north Africa, or the Middle East. And aid agencies say that flight cancellations are hampering efforts to get the disease under control, they rely on commercial flights to get to the infected regions. Liberia's information minister, Lewis Brown, told the Telegraph this week that BA was putting more people in danger. "We need as many airlines coming in to this region as possible, because the cost of bringing in supplies and aid workers is becoming prohibitive," he told the Telegraph. "There just aren't enough seats on the planes. I can understand BA's initial reaction back in August, but they must remember this is a global fight now, not just a west African one, and we can't just be shut out." Christopher Stokes, director of MSF in Brussels, agreed: “Airlines have shut down many flights and the unintended consequence has been to slow and hamper the relief effort, paradoxically increasing the risk of this epidemic spreading across countries in west Africa first, then potentially elsewhere. We have to stop Ebola at source and this means we have to be able to go there.”
  • 4 Temperature screening at airports is an effective way to stop those who have the disease from travelling
    The screening process is pretty porous, especially when individuals want to subvert it. Wake up on the morning of your flight, feel a bit hot, and you definitely don't want to be sent to an isolation booth for days and have to miss your flight. Take an ibuprofen and you can lower your temperature enough to get past the scanners. And if you suspect you have Ebola, you might be desperate to leave, seeing how much better the treatment success has been in western nations. And experts have warned that you cannot expect people to be honest about who they have had contact with. Thomas Eric Duncan, the Ebola victim who died in Texas, told officials he had not been in contact with anyone with the disease, but had in fact visited someone in the late stages of the virus, though he said he believed it was malaria. The extra screening that the US implemented since his death probably wouldn't have singled out Duncan when he arrived from hard-hit Liberia last month, because he had no symptoms while travelling.
  • 5 Border staff should stop people coming in to the country who are at risk
    LEON NEAL via Getty Images
    They're not doctors, and it's a monumental task to train 23,500 people who work for the UK Border Agency how to correctly diagnose a complex disease, and spot it in the millions of people who come through British transport hubs. Public Health England has provided UK Border Force with advice on the assessment of an unwell patient on entry to UK, but they can't be expected to check everyone.
  • 6 Screening at British airports should be implemented to stop unwell people coming in from affected areas
    As mentioned before, the UK, especially London, is a major transport hub. Unlike the US, most of those coming from west Africa will have crossed through Europe, so infected people could be coming from practically anywhere, not just flights directly from those countries. This would require the UK to screen every returning traveller, as people could return to the UK from an affected country through any port of entry. This would be huge numbers of low risk people, at vast, vast expense.
  • 7 Ebola doesn't have a cure
    John Moore via Getty Images
    There are several cures currently being tested for Ebola. They include the ZMapp vaccine which was administered to British sufferer William Pooley and two other Americans who caught the disease in west Africa and they all recovered. Supplies of the drug have now run dry, and it has not been through clinical trials to prove its effectiveness. Mapp Biopharmaceutical, the company that makes ZMapp, says the drug's supplies are exhausted and that it takes months to make even a small batch. But an Ebola cure is very much on the horizon, and would have come sooner had it been seen as any kind of priority for drug companies before it started reaching the western world.
  • 8 Ebola is a death sentence
    It is true that certain strains of Ebola have had a death rate of 90%. However, with this particular epidemic the stats are more positive, a death rate of around 60%. Those who have decent, strong immune systems, are able to access intravenous fluids and scrupulous health care are far more likely to survive, which is why the survival rate of westerners who contract the disease is far better. Experts have suggested that, rather than waste money on pointless airport screenings, funds could be used to improve infrastructure in the affected nations to help halt the spread of the disease at source.
  • 9 Ebola turns you into a zombie
    Renee Keith via Getty Images
    Just, no.