Dementia has many forms and causes. Much progress has been made in dementia research, but scientists still do not understand all of dementia’s causes. Here's what we do know about possible causes and risk factors in different types of dementia.
The Alzheimer’s Association estimates that Alzheimer’s disease (AD) causes 60 to 80 percent of all dementia. The exact cause of AD isn’t known, but several causes are thought to be possible.
Abnormal buildup in the brain
The buildup of two abnormal structures in the brain, called amyloid plaques and neurofibrillary tangles, is common in AD. The buildup may be part of the cause, although scientists are unclear about if these findings could be the result of the disease instead.
Amyloid plaques are clumps of beta-amyloid, a piece of a protein that is found in the normal brain. When these beta-amyloid proteins clump together, they form plaques that can disrupt communication between nerve cells and cause brain inflammation. People with AD have an abundance of these plaques in the hippocampus, the part of the brain involved in memory. The transfer of short-term memories into long-term memories is often disrupted in AD. Learn about other symptoms of Alzheimer’s disease.
Neurofibrillary tangles are fibrous tangles of an abnormal protein called tau. Tau is an important fiber-like protein that keeps microtubules in the brain stable. Microtubules move nutrients, molecules, and information to other cells. When tau is harmfully altered, possibly due to genetic mutation, the fibers get twisted up together. This makes the microtubules unstable and causes them to disintegrate. This effect can collapse the whole neuron transport system.
Some people develop AD as young as their early 30s and 40s. This is called early-onset Alzheimer’s disease. There are three known gene mutations believed to be part of the formation of the amyloid plaques in early onset AD. These three gene mutations do not play a role in the more common type of AD, which is sometimes referred to as late onset Alzheimer’s disease.
AD and other dementias are associated with abnormal structures in the brain called inclusions. These structures are made of various abnormal proteins. It’s not clear whether these structures cause the disease or are caused by the disease.
Lewy body dementia is a common type of progressive dementia. Abnormal structures in the brain called Lewy bodies are characteristic of this disease. They’re found in the brain’s outer layer, called the cortex. The cortex is responsible for thinking, perceiving, producing, and understanding language.
Lewy bodies are also often located in various parts of the brain stem and the substantia nigra. Here, nerve cells release essential neurotransmitters that help control movement and coordination.
Lewy bodies are also commonly found in the brains of people with Parkinson’s disease.
The brain requires constant oxygen from the bloodstream. Without oxygen, brain cells can’t function properly. If the oxygen flow is interrupted long enough, brain cells can die. Any condition that prevents normal blood flow to the brain can cause vascular dementia.
There are several types of vascular dementia. The causes and symptoms for each vary slightly. For example, multi-infarct dementia (MID) is caused by many small strokes in the brain. Dementia is more common when the stroke takes place in the left hemisphere of the brain and when the stroke involves the hippocampus.
Not all people who have a stroke develop vascular dementia.
Frontal lobe dementia is a group of diseases that cause significant changes in behavior or language capability. It’s sometimes known as frontotemporal dementia.
These diseases all involve the degeneration of brain cells located in the frontal and temporal lobes of the brain. The frontal and temporal lobes are the areas of the brain behind the eyes and above the ears. These areas control personality, judgment, emotion, and language.
Frontal lobe dementia rarely involves amyloid plaques but often has neurofibrillary tangles. It can run in families, suggesting that genetics may be an important causal factor.
Pick’s disease is a type of frontal lobe dementia with a strong genetic component. With this disease, your brain has abnormal structures called Pick bodies, made mostly of the protein tau, inside the neurons. Brain cells loaded with Pick bodies tend to balloon up in size and then die. This leads to the characteristic shrinkage, or atrophy, in the frontotemporal regions of the brain.
At the moment, there is no specific treatment for any frontal lobe dementia.
Many causes of dementia and dementia-like symptoms are treatable. They may be reversible if they’re caught early enough and if appropriate treatment is given. Some common reversible conditions include:
Severe vitamin B-6 deficiencies can cause a multisystem illness, known as pellagra, that may include dementia.
Vitamin B-12 deficiencies have been linked to dementia in some cases.
Exposure to lead, other heavy metals, or other poisonous substances can lead to symptoms of dementia. These symptoms may or may not resolve after treatment, depending upon how badly the brain was damaged.
People who have misused substances such as alcohol and recreational drugs sometimes display signs of dementia even after the substance use has ended. This is known as substance-induced persisting dementia.
Metabolic problems and endocrine abnormalities
Prescribed medications can sometimes lead to reactions or side effects called delirium that mimic dementia. These dementia-like effects can occur in reaction to just one drug or they can result from drug interactions. They may have a rapid onset or they may develop slowly over time.
Illegal drug use can also lead to delirium that appears similar to dementia.
Heart and lung problems
The brain requires a lot of oxygen to carry out its normal functions. Conditions such as chronic lung disease or heart problems that prevent the brain from receiving enough oxygen can starve brain cells and lead to the symptoms of delirium that mimic dementia.
Many infections can cause neurological symptoms, including confusion or delirium, due to fever or other side effects of the body’s fight to overcome the infection.
Untreated syphilis can damage the nervous system and cause dementia.
In rare cases, Lyme disease can cause memory or thinking difficulties.
People in the advanced stages of AIDS may develop a form of dementia. People with compromised immune systems, such as those with leukemia or AIDS, may develop an infection called progressive multifocal leukoencephalopathy (PML). PML is caused by a common human polyomavirus called the JC virus. It leads to damage or destruction of the myelin sheath that covers nerve cells. PML can lead to confusion, difficulty with thinking or speaking, and other mental problems.
Subdural hematomas, or bleeding between the brain’s surface and its outer covering (the dura), can cause dementia-like symptoms and changes in mental function.
Anoxia occurs when the brain is starved of oxygen. It may be caused by many different problems. These include:
- heart attack
- heart surgery
- severe asthma
- smoke or carbon monoxide inhalation
- an overdose of anesthesia
Recovery depends upon the duration of the oxygen deprivation.
Brain tumors can damage your brain tissue or create pressure inside your skull. This can limit your brain from functioning normally. Damage or interruption to the brain’s functions can potentially cause dementia.
A stroke happens when blood flow to your brain is blocked. This can nearly double your risk of developing certain types of dementia, especially vascular dementia. Risk factors such as age, sex, and your family history all contribute to your risk of developing dementia after a stroke.
Traumatic brain injuries
Traumatic brain injuries can result from any kind of major impact to your skull. These injuries can cause the proteins in your brain, including beta-amyloid and tau proteins, to function abnormally and cause harm to your brain. This could potentially cause dementia.
Falling down and hitting your head while at home is one of the most common traumatic brain injuries. Hitting your head in a car accident, especially against the windshield in a collision, is another serious cause of dementia. You may be up to five times more likely to develop dementia if you have a traumatic brain injury.
Individuals who have experienced multiple traumatic brain injuries are at even greater risk of developing dementia. They’re at risk for a condition known as chronic traumatic encephalopathy, which is a type of dementia.
There are three types of traumatic brain injuries, measured by their level of severity:
- Mild: These don't cause you to lose consciousness, or they only cause loss of consciousness for less than half an hour. Disorientation, headaches, dizziness, or inability to speak properly last for a few weeks or months at most. The risk of a mild traumatic brain injury causing dementia is low.
- Moderate: These cause you to lose consciousness for a half hour or more. Many of the same symptoms occur as in a mild injury, but they can last for months or longer and be much more severe. The risk of a moderate brain injury causing dementia is much higher.
- Severe: These may cause you to lose consciousness for 24 hours or more. The symptoms of a severe brain injury can be debilitating.
Other conditions that contribute to dementia include:
- Mixed dementia: This happens when several conditions contribute to your dementia. Alzheimer’s disease, Lewy body conditions, and vascular conditions may all be present in a case of mixed dementia.
- Huntington’s disease: This genetic condition causes damage to nerve cells in your spine and brain. You may start to notice symptoms of dementia and cognitive decline after you turn 30 if you have it.
- Parkinson’s disease: The damage to your nerves caused by Parkinson’s can cause dementia.
- Creutzfeldt-Jakob disease: This brain condition is thought to be caused by problems with your brain proteins or by contact with brain or nerve tissue that carries a disease. Symptoms don't often appear until after you turn 60.
These conditions are often caused by a mix of risk factors, including family history and lifestyle choices. Huntington’s disease can only be passed through families and can’t be developed if you don’t have the genes for it.
Some risk factors for dementia can’t be controlled, including:
- your age, as your risk increases after you turn 65
- losing your memory naturally as you age
- Down syndrome, which often causes early onset dementia
- your genes, as a family history of dementia can increase your risk of developing dementia
Other risk factors may respond to lifestyle changes or treatment. These include:
Dementia can be devastating to you and your family as you lose your cognitive function and memory. Seek treatment if you begin to notice symptoms of any form of dementia. Get medical help after an injury or event that causes damage to your brain. Dementia is a progressive condition, so preventive treatment or consistent treatment of causes and symptoms is important. This can help limit the complications you experience or make your symptoms less severe.