Alzheimer’s disease is one of the most feared illnesses of aging. It slowly destroys memory, thinking ability, and independence.
For many years, scientists have focused on abnormal proteins in the brain as the main cause of the disease.
However, a new study suggests that infections and long-term inflammation may also play an important role.
Researchers from Cedars-Sinai have found evidence that a common bacterium best known for causing pneumonia may be linked to Alzheimer’s disease by quietly living in the brain and the eye for years.
The bacterium is called Chlamydia pneumoniae. Most people have never heard of it, but it is actually quite common and can cause respiratory infections such as pneumonia, bronchitis, and sinus infections.
In many cases, the infection is mild and goes away with treatment. But scientists now believe that in some people, the bacteria may not fully disappear. Instead, it may stay hidden in the body and continue to trigger inflammation over a long period of time.
Inflammation is the body’s natural defense against infection or injury. When it happens briefly, it helps healing. But when inflammation continues for years, it can damage tissues, including the brain. Long-term inflammation has already been linked to many chronic illnesses, including heart disease, diabetes, and dementia.
In this study, researchers made a surprising discovery. They found that the bacterium can travel to the retina, the light-sensitive layer at the back of the eye. The eye and the brain are closely connected, and scientists often say the eye is like a window into the brain. Because of this connection, changes in the eye may reflect what is happening inside the brain.
The team examined retinal tissue from more than one hundred people, including individuals with normal thinking ability, mild memory problems, and Alzheimer’s disease.
Those with Alzheimer’s had much higher levels of the bacterium in both their retinas and their brains. People with more bacteria also showed more severe brain damage and worse memory decline.
The researchers also found that people who carry a gene called APOE4, which is known to increase Alzheimer’s risk, were more likely to have high levels of the bacteria. This suggests that some individuals may be especially vulnerable to infection-related damage.
To better understand how the infection affects the brain, the scientists studied human nerve cells in the laboratory and mice that had Alzheimer’s-like symptoms. In both cases, infection led to increased inflammation and greater loss of nerve cells.
The infection also increased production of amyloid-beta, a sticky protein that builds up in the brains of people with Alzheimer’s and is believed to interfere with communication between brain cells.
These findings suggest that infection could speed up the disease process rather than simply occurring alongside it. If the bacteria help drive inflammation and protein buildup, treating the infection early might slow or prevent damage.
The study also highlights the possibility of using eye examinations as a simple way to detect Alzheimer’s risk. Because retinal scans are easier and less invasive than brain scans, they could one day help doctors identify people who may be developing the disease before serious symptoms appear.
In reviewing these findings, the research offers an important new perspective but also raises many questions. The study shows a strong link between the bacterium and Alzheimer’s, but it does not prove that the infection directly causes the disease.
It is possible that weakened brain defenses in Alzheimer’s patients make them more vulnerable to infection, rather than the infection starting the disease itself. More long-term studies in humans will be needed to clarify this relationship.
Even so, the idea that treating chronic infections and reducing inflammation might help prevent or slow Alzheimer’s is exciting.
It opens the door to new treatment approaches, including early use of antibiotics or anti-inflammatory therapies in selected patients. It also reminds us that brain health is closely connected to overall physical health, including the immune system.
If future research confirms these results, it could change how doctors think about Alzheimer’s disease and how it is treated. Instead of focusing only on brain proteins, medical care might also target infections and inflammation throughout the body.
For now, this study provides a hopeful sign that understanding hidden factors like chronic infection may bring us closer to preventing or delaying this devastating illness.
If you care about Alzheimer’s, please read studies about the likely cause of Alzheimer’s disease , and new non-drug treatment that could help prevent Alzheimer’s.
For more health information, please see recent studies about diet that may help prevent Alzheimer’s, and results showing some dementia cases could be prevented by changing these 12 things.
The study is published in Nature Communications.
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