The word dementia is used to describe a group of symptoms – often including, but not limited to, thinking problems, confusion or mood changes. Although often thought of as a disease of older people, it is estimated that around 70,800 people with dementia in the UK are under 65.

What is young onset dementia?

Dementia is caused by underlying diseases that affect how our brain cells work. There are many causes of young onset dementia, with Alzheimer’s disease the most common. The information on these pages will cover different causes of dementia that affect people under 65. You can use the menu below to find out more about different causes of young onset dementia.


Some studies have found that around one in ten people with mild cognitive impairment (MCI) are under the age of 65.

Unlike dementia, symptoms of MCI may not get in the way of a person’s day-to-day life. For some people with MCI, their memory and thinking problems stay the same, but for others they may get worse over time. There are many causes of MCI, some of which are more common in younger people, including:

  • Depression, stress, and anxiety
  • Vitamin deficiencies
  • Thyroid disorders
  • Autoimmune conditions
  • Infections
  • Side effects from medication
  • Sleep disorders like sleep apnoea
  • Early stages of Alzheimer’s disease or another type of dementia


If you are worried about yourself or someone else who may be showing symptoms of dementia or MCI, talk to your doctor. They will be able to rule out other health problems such as vitamin deficiencies that may cause similar symptoms in younger people. They may also refer you to a specialist for further tests if necessary.

Young onset dementia

This leaflet aims to give an introduction to young onset dementia. It’s for anyone who might be worried about themselves or somebody else.

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Alzheimer’s Research UK has a wide range of information about dementia. Order booklets or download them from our online form.

This information was updated in March 2022 and is due to be reviewed in March 2024, it was written by Alzheimer’s Research UK’s Information Services team with input from the Young Dementia Network and lay and expert reviewers. Please get in touch if you’d like a version with references or in a different format.


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Dementia Research Infoline

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