The Reason Memory Fades

A new study shows that contact with common types of infections could be associated with memory problems. However, researchers note that further research is needed to draw concrete conclusions. Lead author, Dr. Clinton Wright, scientific director of the Evelyn F. McKnight Brain Institute at the University of Miami, said, “We are worried about memory decline. 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, researchers looked at brain function tests of 588 older participants to assess memory and thinking ability. In addition, researchers looked for signs of exposure to the bacteria C. pneumonia, which can lead to pneumonia and bronchitis, and H. pylori, as well as to cytomegalovirus and herpes simplex viruses 1 and 2, which cause cold sores and other conditions. About half of the study participants, whose average age was 71, returned five years later for additional tests of mental ability.



Wright notes that just because the person was exposed to the bacteria or virus, it does not mean they became sick 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.



Worse mental performance, including poorer executive function and language performance, was associated with blood tests with increased levels of antibodies. “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 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. Researchers did adjust for 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 is too soon to determine how people who have been exposed to these common infections may be at risk for mental decline and stroke.



“We’re not proving causation. There’s no evidence yet that treating these infections will help,” Wright said. He noted that most participants were Hispanic, so further research in other groups is needed. Because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.






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