The causes of dementia include:

  • Alzheimer’s disease, a brain disease that causes abnormal changes that kill brain cells.
  • Blockages in blood vessels in the brain that limit blood flow to parts of the brain or trigger mini-strokes. These cause a type of vascular dementia known as multi-infarct dementia.
  • Other diseases such as Parkinson’s disease, which affects movement and, later, mental abilities and mood.
  • Serious head injuries.
  • Some brain tumors.
  • Heavy drinking for more than 10 years.
  • An overactive or underactive thyroid gland.
  • Insufficient vitamin B12 levels.
  • Certain brain infections, including infection with HIV (the virus that causes AIDS).
  • Exposure to certain drugs, and reactions to combinations of drugs.
  • The growth of abnormal structures in the brain called Lewy bodies, which causes a form of dementia called Lewy Body Dementia.
  • The shrinking of certain parts of the brain, which causes a less common form of dementia called frontotemporal dementia.

Dementia often has more than one cause. People who have Alzheimer’s disease, for example, may have vascular dementia too.

Alzheimer’s disease and vascular dementia are the most common forms of dementia in older adults. They are not curable. But they can be treated in ways that can improve functioning and quality of life and slow the rate at which symptoms get worse. Alzheimer’s disease accounts for nearly 70% of all cases of dementia. Vascular dementia accounts for more than 10%.  

Risk Factors for Dementia

A risk factor for a health problem is something that increases your risk, or likelihood, of developing that health problem. Simply having a risk factor does not mean you’ll develop the problem. It simply means that you have a higher risk of developing the problem than someone without the risk factor.  The risk factors of Alzheimer’s disease and vascular dementia are somewhat different.

Risk factors for Alzheimer’s Disease

  • Age: While 6% to 8% of adults 65 and older have Alzheimer’s disease, nearly 30% of 85-year-olds do.
  • Family history: About half of those who have a parent or sibling with Alzheimer’s develop the disease by age 90.
  • Depression
  • Down Syndrome
  • Serious head injury
  • Fewer years of formal education
  • Delirium

Some studies suggest that staying mentally, socially, and physically active may lower your risk of developing dementia. Consider joining a book or hiking club (or both); signing up for classes at a nearby college (many schools offer senior discounts on tuition); joining the local YMCA (seniors also get discounts on memberships at many gyms); or volunteering at a local school, hospital, or library.

Risk factors for Vascular Dementia

Most risk factors for vascular dementia are the same as those for heart disease and stroke. These problems make it more likely that blockages will form in your blood vessels and limit or cut off blood flow and oxygen to your brain:

  • High blood pressure 
  • High levels of bad cholesterol (LDL) in your blood and low levels of good cholesterol (HDL)
  • Age: Blood vessels stiffen and narrow as we grow older
  • Smoking
  • Diabetes 
  • A family history of stroke or heart disease
  • Obesity
  • An inactive, sedentary lifestyle
  • High stress levels
  • Strokes

Visit the Prevention section to get easy-to-follow information about living a heart-healthy lifestyle.

Mild cognitive impairment (MCI)

Mild cognitive impairment (MCI) is a condition where people have problems with memory, language, and other mental abilities. These are noticeable and show up on medical tests, but don’t interfere with a person’s daily life. For that reason, MCI isn’t considered a form of dementia. People diagnosed with MCI are at an increased risk of developing dementia.


Last Updated July 2020