2023-05-03 03:30:07
According to a study, frequent infections were associated with poorer cognitive performance in older people. The infections also had an effect on the risk of Alzheimer’s.
A new study by a team led by researchers at the Johns Hopkins Bloomberg School of Public Health found that signs of frequent infection in a sample of middle-aged and older adults were associated with poorer performance on a global cognitive function test. The results add to a growing body of evidence that infections in middle and late life worsen cognitive performance and increase the risk of Alzheimer and other dementias can increase. The study was published in the journal Alzheimer’s & Dementia published.
Herpes virus infections are associated with poor mental performance
For their analysis, the researchers examined the antibody levels against five common pathogens in 575 adults aged 41 to 97 years. The adults were recruited in East Baltimore in 1981 as part of the Epidemiologic Catchment Area Study. The Baltimore study participants donated blood for the tests and underwent cognitive tests at the same time. Antibody tests for pathogens have been conducted, including four Herpesviren – Herpes-simplex-Virus Typ 1, Zytomegalievirus, Varizella-Zoster-Virus (chickenpox and shingles virus) and Epstein-Barr-Virus – as well as the parasite Toxoplasma gondii. The latter is often transmitted to humans through contact with cat feces or by eating undercooked meat.
The research team compared the participants’ blood test results to their performance on the Mini-Mental State Examination—a global cognitive test that assesses things like orientation, attention, language comprehension, memory, and visual perception—and a word recall task that measures memory for a list of words was tested after a 20 minute delay. The researchers found that elevated antibodies to herpes simplex virus type 1 or cytomegalovirus were individually associated with poorer performance on the global cognitive test. In addition, participants with higher numbers of positive antibody tests tended to miss more items on the global cognitive test.
More attention to a controversial topic
“The idea that frequent infections could contribute to cognitive decline and possibly Alzheimer’s risk was once a side issue and remains controversial, but it’s starting to gain more attention based on findings like this study,” says lead author Adam Spira, professor at of the Bloomberg School’s Department of Mental Health and a faculty member at the Johns Hopkins Center on Aging and Health. “After accounting for age, gender, ethnicity, and the major genetic risk factor for Alzheimer’s disease, our study’s data showed that a greater number of positive antibody tests associated with five different infections was associated with poorer cognitive performance. To our knowledge, this type of additive effect of multiple infections on cognitive performance has never been demonstrated.”
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The cause of Alzheimer’s disease remains unclear. Previous research has linked it to infections including herpes simplex virus type 1 and cytomegalovirus. There is also evidence that the protein fragment amyloid-beta, which forms insoluble plaques in the brains of Alzheimer’s patients, acts as an antimicrobial peptide and is secreted at elevated levels by brain cells in response to infection.
Alzheimer’s risk influenced by infections
The pathogens studied in the study often emerge in childhood and are either eliminated or transformed into suppressed, latent infections. Therefore, the researchers considered significant levels of antibodies against these pathogens in the middle-aged and elderly study participants as likely indicators of their reactivation due to age-related weakening of the immune system.
Co-author Brion Maher, a geneticist and professor in the Bloomberg School’s Department of Mental Health, also analyzed the results for participants who shared a common Alzheimer’s risk factor, the Ɛ4 variant of the apolipoprotein E (ApoE) gene. The association between the number of positive antibodies and cognitive status was present in both the Ɛ4 and non-Ɛ4 groups, but was stronger in the non-Ɛ4 group. “It was a surprise to find a weaker link in the Ɛ4 group,” says Maher. “This is something that should be followed up in larger studies.”
This article is based on a press release from the Johns Hopkins Bloomberg School of Public Health. We have the original publication for you here and linked in the text.
Image source: Zachary Kadolph, Unsplash
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