How memories form and how we lose them - Catharine Young
The Surprising Reason Memory Fades
Study finds exposure to common microbes could cause mental decline.
By Mary Brophy Marcus
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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 bacteriaC. pneumoniaeandH. pylori, as well as to cytomegalovirus and herpes simplex viruses 1 and 2.
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C. pneumoniaecan 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 toH. 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.
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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.
"We're not proving causation. There's no evidence yet that treating these infections will help," Wright said.
Dr. Larry Goldstein, director of the Duke Stroke Center in Durham, N.C., said, "This all fits together and makes some sense." He was not involved with the new study.
Goldstein said a variety of infections and inflammatory conditions have been associated with stroke and other vascular disease as well as mental impairment. "There's a big overlap between risk factors for vascular disease and stroke and Alzheimer's disease and cognitive issues," he said. "But right now people can't do a lot about it."
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Study author Wright said in future research, one thing they could ask is who goes on to develop dementia or mental impairment. "But that's not what we did here," he said. "We just looked at crude associations with cognitive performance."
He also noted that the majority of the study participants were Hispanic, so more studies in other groups are warranted.
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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