Exposure to common infections – even if they do not make you ill – may be linked to decline in brain functions like memory and reasoning, according to new research presented at a conference recently. However, the researchers caution more work needs to be done to confirm their findings.

Lead researcher Dr. Clinton Wright, scientific director of the Evelyn F. McKnight Brain Institute at the University of Miami, presented the study at the American Stroke Association’s International Stroke Conference 2014, in San Diego, CA.

He conducted the study with colleagues from Columbia University in New York, NY.

They were interested in further exploring the findings of studies such as that reported in 2013 in the journal Stroke, which found brain function may decline as heart disease risk factors increase. Other studies have also found links between certain infections and increased risk of stroke and Alzheimer’s disease.

“We were very interested in what were the risk factors for cognitive performance and decline,” explains Dr. Wright.

They studied brain function tests and blood sample results from 588 older adults who took part in the Northern Manhattan Study, a research project examining stroke and stroke risk factors in the Northern Manhattan community.

Half of the participants repeated the brain function tests after a 5-year interval.

The results showed links between antibody levels caused by exposure to common infections and worsening cognitive performance in functions like memory, planning and reasoning ability, speed of mental processing and abstract thinking.

The common infections the researchers studied included Chlamydia pneumoniae (which can lead to pneumonia and bronchitis), Helicobacter pylori (the cause of most stomach and duodenal ulcers), and the herpes viruses cytomegalovirus and herpes simplex viruses 1 and 2 (which can cause cold sores and other conditions).

There is evidence that exposure to the infections is linked to increased risk of stroke and atherosclerosis (where arteries become clogged up), and inflammation.

Although he and his colleagues did not explore how exposure to these infections might relate to cognitive decline, Dr. Wright suggests:

It could be caused by an immune system response to the infections or the infection itself could result in clinical damage that we’re not aware of.”

The researchers do not suggest people take action against these infections, as there is no evidence to suggest doing so will do any good. Plus, the infections could have happened decades earlier, and any damage could be the result of a gradual process.

“It would be great if treatment prevented these bad outcomes, but we’re very far away from having that type of evidence,” notes Dr. Wright, who now wants further studies to confirm these findings in other groups, since 70% of the participants in their sample were of Hispanic origin.