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Could Infections Harm Memory in Older Adults?

Early study found connection between exposure to microbes, poorer scores on mental-ability tests

WebMD News from HealthDay

By Mary Brophy Marcus

HealthDay Reporter

THURSDAY, Feb. 13, 2014 (HealthDay News) -- Exposure to several types of common infections could be associated with memory problems, a new study suggests. The authors caution, however, that further research is needed to draw concrete conclusions.

Scientists from the University of Miami and Columbia University in New York City were scheduled to present their research Thursday at an American Stroke Association meeting in San Diego.

"We are worried about memory decline," said lead author Dr. Clinton Wright, scientific director of the Evelyn F. McKnight Brain Institute at the University of Miami. "The findings suggest maybe there is an association with memory decline and exposure to some bacteria and viruses, but we haven't proven it in this study."

For the study, the researchers conducted brain function tests on 588 older participants to assess memory and thinking ability. The investigators also looked for evidence of exposure to the bacteria C. pneumoniae and H. pylori, as well as to cytomegalovirus and herpes simplex viruses 1 and 2.

C. pneumoniae can lead to pneumonia and bronchitis, while herpes viruses cause cold sores and other conditions. For the new study, however, Wright explained that exposure to bacteria or viruses doesn't necessarily mean a person became ill from it.

"Infection is a little bit of a strong term. We measured exposure to these pathogens, but it doesn't mean they became ill. A lot of people are exposed to H. pylori, for example, who never get an ulcer. Just like the common cold, you may or may not be symptomatic," Wright explained.

About half of the study participants -- whose average age was 71 -- returned five years later for additional tests of mental ability.

Blood tests with increased antibody levels were associated with worse mental performance, Wright said, including poorer executive function and language performance.

"We've previously found in other studies that people with greater infectious burden had a higher risk of stroke, and were more likely to have carotid plaque," Wright said. This occurs when fatty substances build up and narrow the carotid arteries, two large vessels that supply oxygenated blood to the brain.

"This time we looked at detailed cognitive [mental function] testing, both at the first time point and then also in a subgroup who we followed up with cognitive testing five years later," he added.

The researchers took into account and adjusted their results for important factors such as age, education, socioeconomics and high blood pressure.

"We are suggesting there is a link with vascular disease, that maybe there's a vascular link to worse cognition through this immune pathway. But the study doesn't explain why the infections are related to worsening cognitive function," said Wright, who added that it's too soon to suggest how it is that people who have been exposed to these common infections may be at risk for mental decline and stroke.

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