Dementia is caused by damage to brain cells. This damage interferes with the ability of brain cells to communicate with each other. When brain cells cannot communicate normally, thinking, behavior and feelings can be affected. The brain has many distinct regions, each of which is responsible for different functions (for example, memory, judgment and movement). When cells in a particular region are damaged, that region cannot carry out its functions normally. The most common causes of dementia include:
Degenerative neurological diseases
- Alzheimer’s disease. This is the most common cause of dementia. Although not all causes of Alzheimer’s disease are known, experts do know that a small percentage are related to mutations of three genes, which can be passed down from parent to child. While several genes are probably involved in Alzheimer’s disease, one important gene that increases risk is apolipoprotein E4 (APOE).
- Parkinson’s disease. A progressive nervous system disorder that affects movement and can also cause dementia. Many people with Parkinson’s disease eventually develop dementia symptoms (Parkinson’s disease dementia).
- Huntington’s disease. Caused by a genetic mutation, this disease causes certain nerve cells in your brain and spinal cord to waste away. Signs and symptoms, including a severe decline in thinking (cognitive) skills, usually appear around age 30 or 40.
- Some types of multiple sclerosis. Dementia-like symptoms can result from fever or other side effects of your body’s attempt to fight off an infection. Multiple sclerosis and other conditions caused by the body’s immune system attacking nerve cells also can cause dementia.
- Creutzfeldt-Jakob disease. A rare, degenerative brain disorder that causes rapid cognitive decline and movement problems.
- Frontotemporal dementia. A type of dementia that primarily affects the frontal and temporal lobes of the brain, leading to changes in behavior and language.
Vascular disorders
- Traumatic brain injury (TBI). This condition is most often caused by repetitive head trauma. Boxers, football players or soldiers might develop TBI. Depending on the part of the brain that’s injured, this condition can cause dementia signs and symptoms such as depression, explosiveness, memory loss and impaired speech. TBI may also cause parkinsonism. Symptoms might not appear until years after the trauma. Traumatic brain injuries may also be caused by car accidents, falls, concussions, etc.
- Infections of the central nervous system. These include meningitis, HIV, and Creutzfeldt-Jakob disease.
- Alcohol-related dementia. A type of brain damage caused by long-term heavy alcohol consumption.
- Certain types of hydrocephalus, a buildup of fluid in the brain
Some reversible causes of dementia include:
- Alcohol or substance use disorder
- Tumors
- Subdural hematomas, blood clots beneath the outer covering of the brain
- Normal-pressure hydrocephalus, a buildup of fluid in the brain
- Metabolic disorders such as a vitamin B12 deficiency
- Low levels of thyroid hormones, called hypothyroidism
- Low blood sugar, called hypoglycemia
- HIV-associated neurocognitive disorders (HAND)
Risk Factors for Dementia
Certain physical and lifestyle factors can raise your chances of dementia, including:
- Age
- Dementia in your family
- Illnesses including diabetes, Down syndrome, multiple sclerosis, heart disease, and sleep apnea
- Depression
- Smoking, heavy alcohol use, poor diet, and lack of exercise
- Brain injury
- Strokes
- Infection of the brain (for example, meningitis and syphilis)
These are just some of the causes of dementia. In some cases, the exact cause of dementia is unknown. It’s important to see a doctor if you or a loved one is experiencing symptoms of dementia.