New research suggests that routine vaccinations could be added to the list of interventions that may prevent dementia. Influenza and pneumonia are leading causes of death in the United States, especially amongst the elderly. In addition to reducing infection-related mortality, there is evidence that vaccines against pneumonia and the flu may also reduce the risk for developing dementia.
In a study examining the medical records of 9,066 adults over age 60, getting a flu vaccine was associated with a 17% reduction in risk for Alzheimer’s disease [1]. Those who got their first flu shot at a younger age, and received the annual vaccine on a regular basis had the most protective benefit. A separate study including 5,146 adults over age 65 found that vaccination against pneumonia before age 75 reduced the risk for Alzheimer’s disease between 25% to 40%, depending on the presence of genetic risk factors [2]. Individuals without the risk genes showed the greatest benefit from vaccination in terms of Alzheimer’s disease prevention.
There is no clear causal relationship between these infectious diseases and Alzheimer’s disease; however, there is evidence that having a severe infection can induce inflammatory changes in the brain that promote neuron damaging processes [3]. Vaccines may then reduce dementia risk by protecting against infection-related brain inflammation. Vaccines train the immune system to respond to certain types of illness-causing viruses and bacteria, which can reduce the chance of getting sick if we are later exposed to these viruses and bacteria [4]. As we age, the immune system’s response to a vaccine weakens, so sometimes the body’s immune response is not strong enough to completely avoid getting sick, but can still offer immense benefit by reducing the severity of the illness. The declining immune response with age is why getting vaccinated starting at a younger age is associated with better protection.
Severe infection can result in an inflammatory response that primes the immune cells in the brain toward a state that makes the brain less resilient and more vulnerable to damage from future stress [3]. There is also evidence that some infection-causing viruses and bacteria can get into brain cells, where they may cause further harm [5].
It should be noted that the pneumonia vaccine does not protect against all causes of pneumonia. Pneumonia is inflammation of the lungs which can result from the infection of lung cells by certain types of bacteria, viruses, and fungi. The pneumonia vaccine protects against the most common strains of the pneumonia-causing bacteria, streptococcus pneumonia. There are two forms of the vaccine: PCV13 protects against 13 strains of bacteria and is typically given to children, while PPSV23 protects against an additional 23 strains and is recommended for adults over age 65, though some people may receive both doses as adults [6].
Another factor contributing to the association between vaccination and reduced dementia risk may be that individuals who receive routine vaccinations are more likely to have access to preventative medical care for other factors that can affect dementia risk, such as cardiovascular health. Overall, this suggests that along with other immune system boosting activities such as maintaining a healthy diet and regular exercise, getting vaccinated against respiratory diseases may help ensure a healthy brain and body throughout life.
Betsy Mills, PhD, is a member of the ADDF's Aging and Alzheimer's Prevention program. She critically evaluates the scientific evidence regarding prospective therapies to promote brain health and/or prevent Alzheimer's disease, and contributes to CognitiveVitality.org. Dr. Mills came to the ADDF from the University of Michigan, where she served as the grant writing manager for a clinical laboratory specializing in neuroautoimmune diseases. She also completed a Postdoctoral fellowship at the University of Michigan, where she worked to uncover genes that could promote retina regeneration. She earned her doctorate in neuroscience at Johns Hopkins University School of Medicine, where she studied the role of glial cells in the optic nerve, and their contribution to neurodegeneration in glaucoma. She obtained her bachelor's degree in biology from the College of the Holy Cross. Dr. Mills has a strong passion for community outreach, and has served as program presenter with the Michigan Great Lakes Chapter of the Alzheimer's Association to promote dementia awareness.
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