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Researchers have found that the virus that causes cold sores, along with other viral or bacterial infections, might be associated with memory loss, and if further studies establish such a link, it could eventually prove helpful in preventing strokes or Alzheimer’s disease.
A long-term study of a group of people in one neighborhood of New York City found that those with higher levels of infection in their blood -- meaning they had been exposed to various pathogens such as the herpes simplex type 1 virus that causes cold sores -- were more likely to have cognitive problems than people with lower levels of infection in the blood. The results, released Monday, are published in the March 26 issue of Neurology, the medical journal of the American Academy of Neurology.
"While this association needs to be further studied, the results could lead to ways to identify people at risk of cognitive impairment and eventually lower that risk," said Dr. Mira Katan, author of the study. "For example, exercise and childhood vaccinations against viruses could decrease the risk for memory problems later in life.”
Katan, who conducted the Northern Manhattan Study at Columbia University Medical Center in New York, is a member of the American Academy of Neurology . The study was performed in collaboration with the Miller School of Medicine at the University of Miami. She said she found the link between infections and memory loss was greater among women, people with lower levels of education and most prominently, in people who do not exercise.
The study, performed in collaboration with the Miller School of Medicine at the University of Miami, tested thinking and memory in 1,625 people from northern Manhattan who had an average age of 69. Participants gave blood samples that were tested for five common low grade infections: three viruses (herpes simplex type 1, which is oral; herpes simplex type 2, which is genital; and cytomegalovirus), chlamydia pneumoniae (a common respiratory infection) and Helicobacter pylori (a bacteria found in the stomach).
The results showed that the people who had higher levels of infection had a 25 percent increase in the risk of a low score on a common test of cognition called the Mini-Mental State Examination.
The memory and thinking skills were tested every year for an average of eight years, but infection was not associated with changes in memory and thinking abilities over time.
"While this association needs to be further studied, the results could lead to ways to identify people at risk of cognitive impairment and eventually lower that risk," said Katan. "For example, exercise and childhood vaccinations against viruses could decrease the risk for memory problems later in life."
Katan, who is currently working at the University of Zurich, in Switzerland, said the study grew out of a previous clinical study of stroke victims that found an association between inflammation in the brain and chronic infections.
“We cannot make any conclusions that infections will lead to cognitive problems, but we think there is a connection,” she said. The issue will require further interactive studies. “If a causal effect is established, it could help in the treatment of dementia and strokes,” she said in a telephone interview with NBC News.com from Switzerland.
William Schaffner, chairman of the department of preventive medicine at Vanderbilt University’s School of Medicine in Nashville, Tennessee, said although the study did not definitively establish a causal association between infections and memory loss, it was “nevertheless provocative and would be worth pursuing fully.
“This will stimulate further research by the neurological and infectious disease communities,” said Schaffner, who was not affiliated with the study.
He noted that already researchers suspected a connection between chlamydia and heart attacks and between the pylori bacteria and stomach cancer. Solid evidence of a connection between infectious diseases and non-communicable illness would be very significant, he said.
“The whole area of connecting infectious diseases to diseases we have not considered infectious is on the cutting edge of research.
“I am intrigued and stimulated by it and it could have very positive implications in preventing diseases,” said Schaffner.
Dr. Alireza Atri, a cognitive neurologist at Massachusetts General Hospital and Harvard Medical School, cautioned the results of the study should be considered preliminary. “There is some plausibility but I would also say that these things (cold sore and herpes viruses) are very common. So it would be rare if older people did not develop antibodies to them.”
He also pointed out the study group was about 80 percent non-white and he would like to see it extended to a larger cross-section of the population. “Can the results be attributed to the general population? Maybe, maybe not,” said Atri.
In an editorial accompanying the study in Neurology, Dr. Timo Strandberg and Dr. Allison Aiello noted there was still much work to be done.
“Undoubtedly, demonstrating that old-age cognitive diseases, including AD, are slowly progressing diseases of viral etiology would revolutionize the dementia research field and be Nobel Prize-worthy,” they wrote. “However, great challenges remain. Such a study is nevertheless worth doing and the editorialists hope that the study… will stimulate this endeavor.”
The study was supported by the National Institutes of Neurological Disorders and Stroke (NINDS), the Swiss National Science Foundation and the Leducq Foundation.