Alzheimer’s disease (AD) is a progressive neurodegenerative condition that destroys memory and thinking skills, eventually leading to the inability to carry out simple tasks. It is the most common cause of dementia globally. Given its impact, a frequent question is whether AD can be caught, like a cold or flu. Determining if Alzheimer’s is communicable or noncommunicable requires understanding how diseases are categorized.
Defining Communicable and Noncommunicable Diseases
Diseases are classified by how they originate and spread. A communicable disease, also known as an infectious disease, is caused by an external pathogen (virus, bacterium, parasite, or fungus). These illnesses are transmissible and spread through contact, air droplets, or bodily fluids. Examples include influenza and measles.
A noncommunicable disease (NCD) is a chronic condition not transmitted from person to person. These long-term illnesses result from genetic predispositions, physiological factors, environmental exposures, and behavioral choices. NCDs, such as heart disease, diabetes, and most cancers, develop internally over a prolonged period.
Alzheimer’s Classification as a Noncommunicable Disease
Alzheimer’s disease is definitively classified as a noncommunicable, neurodegenerative disorder. It originates from internal biological processes within the brain, not from an external infectious agent. The pathology of AD involves the abnormal buildup of two proteins: amyloid-beta and tau.
Amyloid-beta proteins accumulate outside neurons, forming dense clusters known as plaques. Tau proteins aggregate inside brain cells, creating neurofibrillary tangles. This internal pathology disrupts communication between neurons and leads to widespread brain cell death. Alzheimer’s develops slowly and cannot be acquired through casual contact or respiratory exposure.
Understanding the Primary Risk Factors
Since Alzheimer’s disease is not an infection, its development is linked to a combination of non-modifiable and modifiable factors. Advanced age is the greatest risk factor, with most diagnoses occurring after age 65. Genetics also plays a significant role, particularly the presence of the Apolipoprotein E (APOE) gene’s APOE4 variant.
Individuals carrying one copy of the APOE4 allele have a moderately increased risk for AD. Those with two copies face a substantially higher risk compared to the common APOE3 variant. The APOE4 protein promotes the accumulation of amyloid-beta plaques and disrupts the brain’s lipid metabolism.
Beyond genetics, numerous modifiable lifestyle factors influence risk. A high-quality diet, such as the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet, is associated with lower risk. Regular physical activity, aiming for at least 150 minutes of moderate-intensity exercise per week, benefits brain health by supporting cardiovascular function. Avoiding smoking and engaging in cognitively stimulating activities can also help mitigate risk.
Addressing Concerns About Transmission
Public concern about Alzheimer’s transmission often stems from research into the “prion-like” behavior of amyloid and tau proteins. This term refers to how these misfolded proteins induce other normal proteins within the brain to also misfold and propagate from one neuron to the next. This internal, cell-to-cell spread is a mechanism of disease progression, not a form of person-to-person communicable transmission.
Rare, historical instances involved the indirect transfer of amyloid-beta pathology via a no-longer-used cadaver-derived human growth hormone (c-hGH) treatment. This was a unique circumstance linked to a contaminated medical product, not a typical infectious spread. Modern medical and surgical practices, including blood transfusions and the rigorous sterilization of surgical instruments, have shown no evidence of transmitting Alzheimer’s disease. The scientific consensus remains firm that Alzheimer’s disease is a noncommunicable disorder that is not contagious in everyday life.