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Dementia Causes and Risk Factors

Dementia Causes and Risk Factors
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Updated on December 18, 2024
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Dementia occurs when neurons (nerve cells) in the brain stop working, lose connections with other brain cells, and die.

The result is cognitive impairment and other changes that make it difficult for people to function in their daily lives.

The most common cause of dementia is Alzheimer’s disease, which is responsible for 60 to 80 percent of all cases. The other main forms of dementia are vascular dementia, Lewy body dementia, and frontotemporal disorders (also known as frontotemporal dementia).

Researchers believe that dementia may have a strong genetic link but also — with the exception of rare dementias caused by gene mutations — that environment and lifestyle play an important role.

What Are the Causes of Alzheimer’s Disease?

As the leading cause of dementia, Alzheimer’s disease has been the subject of a wide range of research looking into its causes. The following risk factors are linked to Alzheimer’s:

  • Age Most people with Alzheimer’s are 65 or older. Past this age, the risk for Alzheimer’s roughly doubles every five years, according to the Alzheimer’s Association.

  • Family History You’re more likely to develop Alzheimer’s if a parent or sibling is affected by the disease.
  • Genetics Scientists have identified genes that increase the risk of developing Alzheimer’s, as well as genes that directly cause the disease. But less than 1 percent of people with Alzheimer’s have a genetic variant that directly causes the disease.

  • Head Injury Researchers have found a link between head injuries — from car accidents, sports, or falling — and future Alzheimer’s risk.
  • Lifestyle Factors Getting regular exercise and following a healthy diet that is low in sugar and saturated fats and that has plenty of fruits, vegetables, and whole grains may reduce your Alzheimer’s risk.

  • Health Conditions Cardiovascular disease risk factors — including high blood pressure, high cholesterol, and high blood sugar in diabetes — are linked to a greater Alzheimer’s risk.

In Alzheimer’s disease, large numbers of brain cells (neurons) stop functioning and eventually die, causing a loss of brain function over time. While some amount of brain shrinkage is considered a normal part of aging, Alzheimer’s involves much more extensive and rapid loss of brain cells and brain volume.

One hallmark of Alzheimer’s disease is the buildup of two proteins in the brain: beta-amyloid and tau. These proteins form clumps in the brain known as plaques and tangles. Amyloid plaques disrupt communication between neurons, and drugs that reduce these plaques may slow cognitive decline in people with mild Alzheimer’s.

What Are the Causes of Vascular Dementia?

After Alzheimer’s disease, vascular dementia is the most frequent cause of dementia, accounting for about 5 to 10 percent of all cases. But even more people have vascular dementia along with another type of dementia, such as Alzheimer’s; this is called mixed dementia.

Vascular dementia is caused by impaired blood flow to the brain, which prevents brain cells from getting the oxygen and nutrients they need — damaging and eventually killing them. This can happen gradually when small blood vessels become damaged over time, or it can happen more suddenly when a stroke blocks major blood vessels.

The severity of a stroke and its location in the brain will determine its impact on thinking and reasoning. Multiple small strokes may cause damage to different areas of the brain over time.

Risk factors for vascular dementia overlap with those for heart disease and stroke. They include the following:

  • Age Vascular dementia is rare before age 65 but is commonly seen in people who reach their nineties.
  • Health History Previous instances of a heart attack, stroke, or mini-stroke can increase your vascular dementia risk.
  • Atherosclerosis When a combination of cholesterol and other substances (known as plaque) builds up in your arteries, it can limit blood flow to your brain.
  • High Cholesterol Higher levels of LDL (“bad”) cholesterol are linked to a higher vascular dementia risk.
  • High Blood Pressure This condition puts extra stress on blood vessels, potentially damaging them throughout your body, including the brain.
  • Diabetes High blood sugar (glucose) levels can damage blood vessels over time.
  • Smoking By damaging blood vessels, smoking raises the risk for both atherosclerosis and vascular dementia.
  • Obesity Excess body weight heightens the risk of all kinds of vascular disease, potentially leading to vascular dementia.
  • Atrial Fibrillation This form of arrhythmia (abnormal heart rhythm) causes blood clots in the heart that can break off and travel to the brain, leading to stroke and vascular dementia.

What Are the Causes of Lewy Body Dementia?

Lewy bodies are abnormal clumps of the protein alpha-synuclein that accumulate in the brain. Lewy body dementia can develop when these clumps impede normal brain function, affecting thinking, movement, behavior, and mood.

Researchers are still trying to understand what causes Lewy body dementia. They’ve begun to correlate the accumulation of alpha-synuclein with the loss of neurons that produce two important neurotransmitters (brain chemicals): acetylcholine, which plays a key role in learning and memory, and dopamine, which is important for thinking, motivation, mood, movement, and more.

Risk factors for Lewy body dementia include the following:

  • Age People over age 60 are at the greatest risk for Lewy body dementia.
  • Sex Men are more likely than women to develop Lewy body dementia.
  • Family History Your risk is higher if you have a family member with Lewy body dementia or Parkinson’s disease.
  • Diseases and Health Problems People with Parkinson’s disease or REM sleep behavior disorder are at a greater risk.

What Causes Frontotemporal Dementia?

Frontotemporal disorders, commonly called frontotemporal dementia, develop when the frontal (front) and temporal (side) lobes of the brain lose large numbers of neurons. Usually, there’s no clear explanation for why this happens — the only known risk factor is family history.

 Frontotemporal dementia typically affects people at a younger age than other dementia types, with most people affected between ages 45 and 64.

The frontal and temporal lobes are the parts of the brain that are responsible for personality, behavior, and language. This explains why some people with frontotemporal dementia undergo extreme personality changes and become impulsive, emotionally indifferent, or socially inappropriate. Other people lose their capacity to use language.

Scientists have identified abnormal amounts of two proteins — tau and TDP-42 — in the brains of people with frontotemporal dementia. For unknown reasons, these proteins may not work properly and damage neurons in the brain in people with frontotemporal dementia.

Researchers have identified similar changes in genetic expression between frontotemporal dementia and amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease. Investigating those similarities may help scientists better understand and treat both conditions.

When It Isn’t Dementia After All

While dementia often goes unreported and undiagnosed, there are situations in which people who appear to have dementia actually don’t.

That’s because some health conditions — such as depression, delirium, side effects from medications, thyroid problems, certain vitamin deficiencies, and excessive alcohol use — can cause dementia-like symptoms. Unlike dementia, these other causes of dementia-like symptoms may be reversible.

For example, one study found that in a group of nearly 69,000 people diagnosed with dementia, 13 percent had undiagnosed liver cirrhosis, which can cause dementia-like symptoms due to the buildup of toxins in the blood.

While a misdiagnosis of dementia is possible, it’s likely that many people with dementia go undiagnosed, according to the Penn Memory Center. Reasons for this lapse can include doctors not recognizing symptoms, patients not sharing cognitive difficulties with their doctor, and a hesitance among some doctors to make a diagnosis that may be devastating or have no clear course of treatment.

The Takeaway

  • While different types of dementia follow different patterns, a common feature is the loss of brain cells.
  • You may be able to reduce your overall dementia risk through healthy lifestyle measures, but some dementia types have no known modifiable causes.
  • Other possible causes of dementia include inherited genes, head injuries, and health conditions like cardiovascular disease.
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David Weisman, MD

Medical Reviewer

David Weisman, MD, is the director of the Clinical Trial Center at Abington Neurological Associates in Pennsylvania, where he has conducted numerous clinical trials into mild cognitive impairment and Alzheimer’s disease to develop disease-modifying drugs.

Dr. Weisman has dedicated his research career toward advancing new therapies for Alzheimer’s disease, focusing on clinical trials for the prevention and treatment of Alzheimer’s disease, mild cognitive impairment, and other dementias, and he devotes his clinical practice to memory and cognitive problems.

He received a bachelor's degree in philosophy from Franklin and Marshall College, then an MD from Penn State College of Medicine. After an internship at St. Mary’s Hospital in San Francisco, he completed his neurology residency at Yale, where he served as chief resident. He then went to the University California in San Diego for fellowship training in Alzheimer’s disease and other dementias.

Weisman has published papers and studies in journals such as Neurology, JAMA Neurology, Stroke, and The New England Journal of Medicine, among others.

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Pamela Kaufman

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Pamela Kaufman assigns and edits stories about infectious diseases and general health topics and strategizes on news coverage. She began her journalism career as a junior editor on the health and fitness beat at Vogue, followed by a long stint at Food & Wine, where she rose through the ranks to become executive editor. Kaufman has written for Rutgers University and Fordham Law School and was selected for a 2022 Health Journalism Fellowship from the Association of Health Care Journalists and the Centers for Disease Control and Prevention (CDC).

Kaufman enjoys going on restaurant adventures, reading novels, making soup in her slow cooker, and hanging out with her dog. She lives in New York City with her husband and two kids.

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Resources
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  2. What Are the Causes and Risk Factors of Alzheimer's and Other Dementias? Alzheimer’s Association.
  3. Can Alzheimer's Disease Be Prevented? Alzheimer’s Association.
  4. What Happens to the Brain in Alzheimer's Disease? National Institute on Aging. January 19, 2024.
  5. Vascular Dementia. Alzheimer’s Association.
  6. Vascular Dementia. Mayo Clinic. July 29, 2021.
  7. What Is Lewy Body Dementia? Causes, Symptoms, and Treatments. National Institute on Aging. July 29, 2021.
  8. Lewy Body Dementia. Mayo Clinic. June 2, 2023.
  9. Frontotemporal Dementia. Mayo Clinic. November 28, 2023.
  10. What Are Frontotemporal Disorders? Causes, Symptoms, and Treatment. National Institute on Aging. July 30, 2021.
  11. Silvey S et al. A Possible Reversible Cause of Cognitive Impairment: Undiagnosed Cirrhosis and Potential Hepatic Encephalopathy in Patients with Dementia. American Journal of Medicine. November 2024.
  12. Stigma Causes Underdiagnosis in Dementia. Penn Memory Center. March 8, 2023.