Can You Catch Alzheimer's And Other Forms of Dementia?

New findings from the Northern Manhattan Study (NOMAS) suggest that loss of cognitive abilities with age may be related to repeated infections.

Dr. Mira Katan, a physician and lead researcher for the study, says that infections may contribute to a kind of “common ground” between the two most common causes of intellectual decline in the elderly, vascular disease and dementia.

What We Already Know About Age-Related Cognitive Decline

Medical science emphasizes two types of intellectual impairment in the elderly. Vascular disease can be thought of as a kind of “plumbing problem.” In older people who have had brain injuries or mini-strokes, tiny areas of damaged tissue can accumulate in the brain. The process of inflammation removes damaged brain tissue, but removes surrounding, healthy brain tissue with it. Eventually so much of the brain can be destroyed that mental functioning is impaired. This form of age-related cognitive impairment is diagnosed along a spectrum from relatively mild to relative severe symptoms: mild vascular cognitive impairment, vascular dementia due to a single infarct (clot causing death of brain tissue), multi-infarct dementia, vascular dementia due to lacunar lesions (essentially “holes” in the functional tissue of the brain), vascular dementia due to hemorrhagic lesions (bleeding in the brain), Binswanger disease (causing destruction of the larger blood vessels in the brain), and subcortical dementia.

There can also be mixed dementia, attributable to a combination of vascular problems and the more common source of intellectual impairment in the elderly, Alzheimer’s disease. In Alzheimer’s, tangles of proteins (usually) “strangle” neurons so that the brain slowly loses connections and memory and movement are lost.

The NOMAS study suggests that there is a third category of age-related intellectual decline “in between” vascular dementia and Alzheimer’s. Very specific infections have been tied not just to age-related problems in cognition but also to stroke.

Zeroing In On Brain-Specific Infections

Between 1993 and 2001, Dr. Katan and her colleagues recruited 1625 residents of the northern reaches of the island of Manhattan in New York City. All of the participants in the study were free of stroke, 58 percent were Hispanic, and 65 percent were women. Their average was 69 years when they joined the study.

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The NOMAS team assessed intellectual function when participants were brought into the study with the Mini-Mental State Examination (MMSE), and once a year with a quiz that could be administered by telephone. At the beginning of the study, the researchers also took blood samples to measure cumulative exposure to common infections including Chlamydia, herpes (both oral and genital), cytomegalovirus (CMV), and Helicobacter pylori, a common bacterial infection of the stomach and duodenum. The researchers also did genetic testing to determine the APOE genotype, which indicates some of the links between diet and vascular health and also future risk of Alzheimer’s disease.

Certain Infections Cancel Out Benefits Of Good Genes And Good Diet In The Aging Brain

Dr. Katan’s group found that there was a link between history of infections and mental status that wasn’t changed by genetics (and, by extension, good diet). Elderly people who had a history of viral infection were more likely to achieve lower scores on the MMSE used to measure mental status. It didn’t make a difference how many times they had had viral infections, and the study did not have a way to find the relative important of different viral infections, but there was no doubt that exposure to herpes (either herpes-1, the more commonly “genital” form of the disease, or herpes-2, the viral infection more commonly associated with cold sores) or cytomegalovirus (CMV) went hand in hand with decreased mental function in old age.

How Does Viral Infection Impair Brain Function?

Dr. Katan surmised that chronic viral infection could cause chronic inflammation of blood vessels in the brain. She also believes it is possible that viruses attack brain tissue directly, but nothing in the study could confirm this.

Katan also noticed that there was an interaction between the severity of the effects of viral infection and physical activity. Women who were less physically active suffered greater mental impairment. It might be, she speculated, that even if you have a long history of viral infections, exercise might reduce the impact of those infections on your brain. Exercise may protect against the effects of infection on the brain.

What Does This Study Suggest for Preserving Brain Health?

There’s general agreement among neurological researchers that the findings of Dr. Katan and her coworkers may “revolutionize” the field. Among the very first studies that may get funding is a test of a herpes medication, Valacyclovir, in people who have Alzheimer’s disease. Of course, the way studies work, the people who will be included in the study first are those who have the least to lose. It may be many years before researchers test the possibility that treating herpes infections in people who do not yet have vascular dementia or Alzheimer’s disease may prevent vascular dementia or Alzheimer’s disease.

That doesn’t mean you can’t ask your doctor for treatment if you know you have been exposed to the virus – and nearly 90 percent of the American population has been exposed to either the cold sores virus or genital herpes, or both.

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There have also been studies that have found an unexpected useful role of antibiotic treatment for traumatic brain injuries. For reasons that are not entirely understood, chronic use of the antibiotic minocycline (more often used to treat acne), seems to reduce the progression of mental impairment after traumatic brain injury in football players, soldiers, and boxers. At least a few doctors are using minocycline as a preventive treatment in people at special risk for stroke, or with a history of stroke, or a strong family history of Alzheimer’s.

Age-related cognitive decline also responds to moderation in diet and regular exercise. Your best bet, if you are approaching the age Alzheimer’s and vascular dementia are a personal concern, is to find a holistically oriented doctor and to work to keep your brain in shape. There are multiple strategies for brain health. Each may help. Using them together, you may be able to avoid age-related cognitive decline.