What Causes Dementia?

Dementia is caused by diseases or injuries that damage brain cells and interfere with memory, thinking, communication, or everyday activities. Alzheimer’s disease is the most common cause, while strokes and damaged brain blood vessels can lead to vascular dementia. Other causes include Lewy body disease and frontotemporal disorders. Age raises risk, but dementia is not an inevitable part of getting older, and some conditions can cause similar symptoms.

How does dementia develop?

Dementia is a general term for a decline in memory, thinking, language, judgment, or other mental abilities that becomes serious enough to interfere with daily life. It is not a single disease. Instead, it results from different conditions that damage the brain or disrupt how brain cells communicate.

In many forms of dementia, brain cells gradually stop working properly, lose their connections with other cells, and eventually die. The parts of the brain affected determine which abilities change first. For example, damage to areas involved in forming memories may lead to forgetfulness, while damage affecting language or behavior may cause different early changes.

According to the World Health Organization (WHO), several diseases and injuries can cause dementia. Alzheimer’s disease is the most common form, accounting for an estimated 60% to 70% of cases worldwide. Different forms can also occur together, making the underlying causes more complex.

What diseases cause dementia?

The main causes differ in how they affect the brain. Identifying the underlying disease helps healthcare professionals understand changes in memory and behavior and plan appropriate care.

Alzheimer’s disease

Alzheimer’s disease is the leading cause of dementia, particularly among older adults. It involves abnormal changes in proteins within and around brain cells. A protein called beta-amyloid can form plaques between cells, while another protein called tau can form tangles inside them. These changes are associated with damage to brain cells and the connections that allow them to communicate.

Scientists do not yet fully understand why Alzheimer’s disease develops in most people. Age-related changes, genetic factors, and other health and environmental influences may contribute. According to the National Institute on Aging (NIA), age is the strongest known risk factor for Alzheimer’s disease, but younger adults can also develop it.

Vascular dementia

Vascular dementia develops when problems with the blood supply to the brain damage brain tissue. Brain cells need a steady supply of oxygen and nutrients carried by the blood. When blood flow is interrupted or reduced, those cells may become damaged or die.

Possible underlying problems include a major stroke, several smaller strokes, or narrowing and blockage of small blood vessels in the brain. Conditions affecting blood vessels, including high blood pressure and diabetes, can increase the risk of this type of damage. However, having a stroke does not necessarily mean someone will develop dementia.

The National Health Service (NHS) explains that vascular dementia can follow a major stroke or result from widespread damage caused by smaller strokes and blood vessel disease. Changes may appear after a stroke or develop gradually as blood vessel damage accumulates.

Dementia with Lewy bodies

Dementia with Lewy bodies is associated with abnormal deposits of a protein called alpha-synuclein inside brain cells. These deposits, known as Lewy bodies, interfere with normal cell function and communication. The condition can affect thinking, attention, movement, sleep, and visual perception.

Its precise cause is not fully understood. The condition is related to Parkinson’s disease, and some people experience movement difficulties alongside changes in thinking. The pattern and timing of these changes can help clinicians distinguish it from other forms of dementia.

Frontotemporal dementia

Frontotemporal dementia results from damage to the frontal and temporal lobes, areas of the brain involved in behavior, personality, language, and decision-making. Abnormal protein changes are associated with the loss of nerve cells in these regions.

Unlike many other common forms of dementia, frontotemporal dementia often affects people in midlife. It is frequently diagnosed between ages 45 and 65, although it can occur outside this age range. Some forms have a stronger inherited component than other common dementias.

Mixed dementia

Some people have more than one disease contributing to their cognitive changes. This is called mixed dementia. A common combination is Alzheimer’s disease and vascular dementia, in which both changes associated with Alzheimer’s and damage to the brain’s blood vessels affect thinking and memory.

Mixed dementia can be difficult to identify because the effects of each disease may overlap. According to MedlinePlus, a service of the U.S. National Library of Medicine, healthcare professionals may use medical history, cognitive assessments, physical examinations, blood tests, and brain imaging to help determine the causes of cognitive difficulties.

Less common causes

Several less common diseases and conditions can cause dementia or progressive problems with thinking. These include Huntington’s disease, certain forms of brain degeneration, chronic traumatic encephalopathy associated with repeated traumatic brain injuries, and some infections affecting the brain. Normal pressure hydrocephalus, which involves a buildup of cerebrospinal fluid in the brain, can also produce dementia-like difficulties and may respond to treatment.

These conditions have different underlying mechanisms and may require different investigations. The presence of memory or thinking problems alone does not establish which disease, if any, is responsible.

What increases the risk of developing dementia?

A cause is the disease or injury responsible for brain damage, whereas a risk factor increases the likelihood of developing a condition. Many people have several risk factors without developing dementia, and some people develop dementia without an obvious history of them.

The World Health Organization identifies several factors associated with an increased risk of dementia. These include:

• Increasing age: Dementia becomes more common as people grow older, especially after age 65. However, it is not an inevitable consequence of aging.
• Genetic factors and family history: Certain inherited gene changes can cause specific forms of dementia, while other genetic variations may influence risk. Most cases are not explained by a single inherited gene change.
• Cardiovascular and metabolic conditions: High blood pressure, diabetes, high blood sugar, and excess body weight are associated with a higher risk. Some of these conditions can contribute to damage affecting the brain’s blood vessels.
• Smoking and harmful alcohol use: These behaviors are associated with a higher risk of dementia and can also harm general health.
• Physical inactivity: Low levels of physical activity are associated with a greater risk of cognitive decline and dementia.
• Hearing and vision loss: These sensory changes are associated with dementia risk, although their relationships with the disease are complex.
• Depression and poor sleep: Both have been linked to dementia risk, but their relationship with cognitive decline can vary. Depression and sleep problems can also affect thinking independently of dementia.
• Social isolation and environmental factors: Limited social engagement and exposure to air pollution are among the factors associated with increased risk.
• Head injuries and stroke: Traumatic brain injuries and cerebrovascular events can damage the brain and increase the likelihood of later cognitive problems.

These associations do not mean that any single factor inevitably causes dementia. Some risks can be reduced through changes in health behaviors or management of existing medical conditions, while others, such as age and certain inherited genetic factors, cannot be changed.

Can dementia run in families?

Yes. Some forms of dementia have a genetic component, but a family history does not automatically mean that other relatives will develop the condition. In most people with Alzheimer’s disease, risk reflects a combination of genetic, biological, environmental, and lifestyle influences rather than one inherited cause.

Rare changes in particular genes, including APP, PSEN1, and PSEN2, can cause inherited forms of Alzheimer’s disease that often begin before age 65. Other genetic variations may increase susceptibility without determining whether someone will develop dementia. Familial forms of frontotemporal dementia can also occur.

When several close relatives develop dementia at unusually young ages, a healthcare professional may recommend a review of the family history and, in selected circumstances, genetic counseling. Genetic testing is not necessary or appropriate for everyone with a family history of dementia.

Can other conditions cause memory problems that resemble dementia?

Yes. Not every problem with memory or concentration is caused by a progressive brain disease. Certain medical conditions, medication effects, sleep problems, and mental health conditions can produce similar difficulties. Some improve when the underlying cause is identified and treated.

The National Institute on Aging notes that potential causes of memory problems include:

• Vitamin B12 deficiency and other nutritional problems.
• Thyroid, kidney, or liver disorders.
• Side effects from certain medicines or combinations of medicines.
• Depression and anxiety.
• Alcohol or drug misuse.
• Sleep disorders.
• Brain infections, tumors, blood clots, or head injuries.

These conditions do not all cause true dementia. Some interfere with memory temporarily, while others may cause persistent cognitive problems or occur alongside a brain disease. A clinical assessment helps distinguish among these possibilities.

Delirium is another important distinction. It involves a sudden change in attention, awareness, or thinking and can be caused by an acute illness, infection, medication effect, or another medical problem. A sudden change in mental state needs prompt medical assessment rather than being assumed to be dementia.

Can dementia be prevented?

There is no guaranteed way to prevent every form of dementia. However, managing certain health conditions and maintaining healthy behaviors may reduce the risk of cognitive decline. Actions that support overall brain and cardiovascular health include:

• Keeping blood pressure, blood sugar, and cholesterol under appropriate medical management.
• Staying physically active according to individual abilities and health needs.
• Eating a balanced, varied diet.
• Avoiding smoking and harmful alcohol use.
• Addressing hearing or vision difficulties with appropriate care.
• Maintaining social connections and taking part in mentally engaging activities.
• Seeking help for persistent sleep problems and depression.

These steps support general health and may help lower dementia risk, but they cannot eliminate it. Evidence for risk reduction is stronger for some factors than for others, and the effect of any individual change can vary.

When should memory changes be evaluated?

Arrange a medical evaluation when changes in memory, language, judgment, or behavior persist, worsen, or begin to interfere with ordinary activities. For example, a person may increasingly struggle to manage familiar tasks, follow conversations, make decisions, or remember recent events. These experiences can have several causes and should be considered in context.

A healthcare professional will usually ask when the changes began, how they have progressed, which daily activities are affected, and whether there is a relevant medical or family history. A review of medicines, a physical and neurological examination, cognitive testing, blood tests, and brain imaging may help identify the underlying cause. A family member or caregiver who has noticed changes can provide useful information.

Finding the cause matters because different forms of dementia may need different approaches to care, and some conditions that resemble dementia may improve with appropriate treatment. Even when a progressive brain disease is responsible, early assessment can help people and families plan for support and discuss available treatment options.