Scientists have long used vaccines to protect people from infectious diseases. However, researchers are now discovering that some vaccines may do much more than prevent infections.
A new study led by Mass General Brigham suggests that the Bacillus Calmette-Guérin (BCG) vaccine, which has been used for more than 100 years to protect against tuberculosis, may also influence the brain’s immune system and possibly help lower the risk of Alzheimer’s disease.
The research was published in the journal Communications Medicine.
Alzheimer’s disease is the most common cause of dementia. It slowly destroys memory, thinking, and the ability to carry out everyday activities.
One of the biggest challenges is that harmful changes inside the brain begin many years before symptoms appear. Scientists are therefore searching for ways to protect the brain before permanent damage develops.
The BCG vaccine is already widely used around the world to prevent tuberculosis. Earlier studies suggested that people who received BCG appeared less likely to develop Alzheimer’s disease, but researchers did not know why.
The new study aimed to uncover the biological explanation.
The research team followed 23 adults aged 55 years and older for one year. Twelve participants already had biological signs linked to Alzheimer’s disease, while 11 did not. The researchers regularly collected blood samples and cerebrospinal fluid, the clear liquid that surrounds the brain and spinal cord, to see how the immune system responded after vaccination.
The results showed that BCG changed the activity of immune cells surrounding the brain. These immune cells became more responsive when faced with new challenges, suggesting that the vaccine trained the immune system to react more effectively.
Importantly, this stronger immune response did not increase harmful inflammation, which is known to contribute to brain damage and neurodegenerative diseases.
The scientists also measured amyloid-beta, a protein closely linked with Alzheimer’s disease. In participants who did not already show Alzheimer’s-related brain changes, amyloid levels decreased in the fluid surrounding the brain while increasing in the bloodstream. This pattern suggests that the protein may have been cleared from the brain more efficiently.
However, participants who already had Alzheimer’s-related pathology did not experience the same changes, suggesting that the vaccine may work best before the disease becomes established.
Senior researcher Dr. Steven Arnold explained that the findings support the idea that the immune system and the brain are much more closely connected than previously believed. The researchers hope future studies will determine whether BCG can help preserve brain health before Alzheimer’s disease develops.
The study builds on many years of BCG research. Scientists have previously found that the vaccine may provide unexpected health benefits beyond preventing tuberculosis, including improving immune function and lowering the risk of certain diseases.
This phenomenon is sometimes called trained immunity, where the immune system becomes better prepared to respond to different threats.
Although the results are encouraging, the researchers stress that this was a small study involving only 23 participants, and everyone received the vaccine without a placebo comparison group. Larger randomized clinical trials are still needed to confirm whether BCG truly lowers Alzheimer’s risk and to identify who might benefit the most.
Overall, the findings provide an interesting new explanation for earlier observations linking BCG vaccination with a lower risk of Alzheimer’s disease. While the vaccine should not yet be viewed as a treatment or prevention strategy for Alzheimer’s, it opens an exciting new area of research that could one day lead to better ways of protecting brain health as people age.
If you care about brain health, please read studies about vitamin D deficiency linked to Alzheimer’s and vascular dementia, and higher magnesium intake could help benefit brain health.
For more information about brain health, please see recent studies about antioxidants that could help reduce dementia risk, and coconut oil could help improve cognitive function in Alzheimer’s.
