Causes and Risk Factors of Alzheimer’s Disease

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Alzheimer’s disease is a neurological condition that is characterized by changes in the brain.

These changes include brain atrophy, or shrinkage, and a build-up of amyloid and tau proteins in the brain. The accumulated amyloid protein can form abnormal clumps in the brain, known as amyloid plaques. In contrast, excess tau protein forms tangled fibers in your brain cells, known as neurofibrillary tangles.

These tangles and plaques can damage brain cells, known as neurons, particularly in the part of the brain that controls memory. This can prevent neurons from sending messages to each other, interfering with functions such as thinking, remembering, learning, and planning, and eventually leading to dementia

These changes in the brain can sometimes begin 10 years before any symptoms of Alzheimer’s disease appear. Over time, the condition spreads to other parts of the brain and results in a loss of neurons, causing the brain to atrophy. 

These neurological changes are caused by age-related degeneration and other genetic, physical, and lifestyle factors. The role that these factors play in the risk of Alzheimer’s disease can vary from person to person. However, the exact causes of this condition are not fully understood yet. 

Brain & Body Risk Factors

Aging is a major risk factor for Alzheimer’s disease as it causes changes in the brain. Other health conditions and head trauma can also raise your risk of developing Alzheimer's.

Aging

Aging is perhaps the most significant risk factor of Alzheimer’s disease. After the age of 65, the number of people with Alzheimer’s disease doubles every five years.

While aging does not cause Alzheimer’s and many people live till 90 and beyond without developing any form of dementia, roughly one-third of all people over the age of 85 may have this condition. 

These are some of the age-related changes that may occur in the brain: atrophy, inflammation, vascular damage, and increased production of unstable molecules known as free radicals. 

These changes affect neurons in the brain and contribute to the progression of Alzheimer’s disease. Alzheimer’s is not a normal part of aging, however. The brain shrinks considerably as the condition progresses.

Health Conditions

The following health conditions can also raise your risk of Alzheimer’s disease:

  • Diabetes
  • Heart disease
  • High blood pressure
  • High cholesterol
  • Obesity

These conditions can reduce the rate at which the brain is able to clear out excess amyloid protein, leading to a build-up of protein in the brain. These conditions pose more of a risk to those who are 50 and older.

Mild Cognitive Impairment

Mild cognitive impairment (MCI) is a condition marked by cognitive decline, which can affect functions like thinking, memory, and language. This decline is often greater than normal for the person’s age, but not as severe as the decline associated with dementia. A person with MCI can still function in work or social environments. 

MCI can sometimes be an early sign of Alzheimer’s disease and dementia. If a person with MCI is primarily experiencing memory loss, there is a significant risk of eventually being diagnosed with Alzheimer’s disease.

Everyone who has MCI doesn't necessarily develop Alzheimer’s disease or dementia. However, being diagnosed with MCI can encourage healthier lifestyle choices, help you develop strategies to cope with the memory loss that accompanies these conditions, and ensure that you see your healthcare provider regularly to monitor your symptoms.

Head Trauma

Having a head injury that caused trauma to the brain can raise the risk of developing Alzheimer’s disease. Severe injury, multiple injuries, or getting injured after the age of 50 can further increase the chances of developing Alzheimer’s.

Family History & Genetics

The role of genes in Alzheimer’s disease is complex and still being investigated. 

The risk of developing Alzheimer’s disease is higher if your parents or siblings have had it; however, having a family history of the condition doesn’t guarantee that you’ll have it too. If several people in your family have had Alzheimer’s, particularly at a younger age, you should consider genetic counseling to evaluate your chances of developing it.

There are two types of Alzheimer’s disease; both types have genetic risk factors associated with them:

  • Early-onset Alzheimer’s disease: This is a rare form of the condition, where symptoms can appear at any time after the age of 30. Inheriting a genetic mutation in one of three genes can lead to early-onset Alzheimer’s disease. 
  • Late-onset Alzheimer’s disease: This is the more common form of the condition, where symptoms first appear in the mid-60s. People with a gene variant known as APOE ɛ4 on chromosome 19 may be more likely to develop late-onset Alzheimer’s disease. However, having the variation doesn’t mean you’ll definitely develop Alzheimer's, and some people with Alzheimer’s don’t have APOE ɛ4.

Having Down syndrome, a genetic chromosome disorder, can also raise your risk of developing Alzheimer’s disease. This is because people with Down syndrome have an extra copy of chromosome 21, so they have an additional gene producing the protein that leads to the production of beta-amyloid.

People with Down syndrome exhibit symptoms of Alzheimer’s 10 to 20 years before other people usually do.

Lifestyle Risk Factors

Other lifestyle, developmental, and environmental factors can also affect your brain and raise your risk of Alzheimer’s disease. These include:

There are steps you can take to keep your brain and body healthy, in order to prevent cognitive decline and lower your chances of developing Alzheimer’s disease and dementia:

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  1. Ramos-Cejudo J, Wisniewski T, Marmar C, et al. Traumatic brain injury and Alzheimer's disease: the cerebrovascular link. EBioMedicine. 2018;28:21-30. doi:10.1016/j.ebiom.2018.01.021

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