Washington, Feb 14 (IANS): An exposure to common infections like cold sores, mild pneumonia or stomach discomforts - even if the infections never made you ill - may increase risk of memory decline, shows new study.

Researchers found that exposure to Chlamydia pneumoniae, Helicobacter pylori, cytomegalovirus and herpes simplex viruses was associated with worse cognitive performance, including memory, speed of mental processing, abstract thinking and planning and reasoning ability.

"We were very interested in what were the risk factors for cognitive performance and decline," said Clinton Wright, scientific director of the Evelyn F. McKnight Brain Institute at the University of Miami in the US.

Earlier studies have already linked certain infections to an increased risk of stroke and Alzheimer's disease.

Researchers investigated if evidence of past exposure to these infections contributed to performance on tests of memory, thinking speed and other brain functions.

The study conducted brain function tests and took blood samples from 588 people. Half of the participants then took cognitive tests again in five years.

"The poor cognitive function 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," he explained.

Wright, however, does not suggest that people plan any major action to combat these infections.

There is no evidence yet that treating these infections is beneficial because the initial exposure to the viruses may have happened decades earlier and the damage may be the result of a gradual process, said the research presented at the American Stroke Association's International Stroke Conference 2014.