Understanding Mental Capacity in Dementia

  • Catrin Emily Jones Bachelor of Science - BS, Psychiatric/Mental Health Nurse/Nursing, Swansea University, UK
  • Jason Ha Bachelor of Medicine, Bachelor of Surgery - MBBS, University of Bristol


Definition of mental capacity 

A person’s mental capacity refers to their ability to understand and use information to make decisions about their life. It also pertains to that person’s ability to communicate decisions about their life. However, mental capacity is not a “blanket statement”; if a person is deemed to lack capacity about one decision, this does not mean they cannot make any decision about their life. 

Significance in dementia 

When the memory of a person with dementia deteriorates, it is possible that they become unable to make certain decisions for themselves. When this happens, the person with dementia is deemed to lack the mental capacity to decide at this time. 

Knowing the mental capacity of a person with dementia is significant because the right to make one’s own decisions is fundamental to human autonomy. Liberty is a human right, and it should not be assumed that a person is unable to contribute to their care plan because they have a cognitive illness such as dementia. Dementia patients deserve the opportunity to have a say in changes made to their lives. Therefore, it is morally correct to complete a mental capacity assessment. 

Stages of dementia 

Early stage 

Dementia is a progressive condition, which means that it worsens over time. Currently, there is no cure for dementia; instead, available medical treatments only aim to decelerate the condition’s progression. The pace at which dementia advances is dependent on multiple factors, such as: 

  • The type of dementia
  • Age
  • Mental health 
  • Physical health
  • Personal lifestyle

Generally, dementia progression is categorized into three stages: mild (early), moderate (middle), and severe (late). That said, dementia affects every person differently; therefore, it is not a linear condition. Although it is rare, a mild case of dementia can develop and deteriorate rapidly. 

Typically in the mild stage of dementia, the individual will begin to experience cognitive issues that impact their everyday living. These issues relate to their memory and attention, personality and behavior changes, planning and problem-solving, as well as language and communication. 

There are several types of dementia; the most common are Alzheimer’s disease, vascular dementia, and Lewy body dementia

Impact on mental capacity 

When dementia progresses, many people suffering from it will need support making decisions about their health, care, finances, and living arrangements. 

Questions regarding mental capacity are frequent when discussing dementia.

Due to the disease’s progression, it can be difficult to identify the moment when an individual with dementia is no longer mentally capable of making a specific choice. The individual’s presentation may elicit mixed perceptions. For example, the individual may appear as “slightly capable” or “likely incapable”; however, they are fully aware of the issues relating to the decision. 

Moreover, the person’s cognitive abilities are prone to fluctuate. Therefore, they may present as more confused today, whereas they are more oriented tomorrow. A lack of capacity is not always a permanent condition. In such cases, the result that a person with dementia lacks mental capacity regarding a decision may need to be revised on the following day. 

Recognizing cognitive changes 

A person’s cognition is their mental process of gaining knowledge and comprehension. Some of the many cognitive processes include: thinking, remembering, judging, knowing, and problem-solving. A cognitive change, therefore, refers to any of these processes being impacted by factors such as a disease or even age, often resulting in a decline. 

Cognitive changes in dementia can include all of the cognitive processes listed above in addition to talking (word-finding difficulties) and disorientation (the state of uncertainty of time, place, and person). 

As dementia is in the early stage, the family, friends, or loved ones would likely notice these problems before the impacted person. For example, a person with dementia may start misplacing belongings or become repetitive in conversations without realizing it. 

Factors influencing mental capacity 

Biological factors

To begin with, any abnormalities within the brain’s anatomy or chemistry can affect its functioning and mood regulation, possibly resulting in mental incapacity. 

Age may affect the risk and onset of certain mental health difficulties, which, if progressive conditions such as dementia, could impact the individual’s decision-making abilities. 

Moreover, mental illness may run in families and be hereditary; thereby, the diagnosis is influenced by genetics.

Brain changes 

A person’s mental capacity can be impacted by several types of brain disturbances or impairments, including dementia, stroke, brain tumor, traumatic brain injuries, as well as mental illnesses like depression and schizophrenia.

Assessment of mental capacity 

The Mental Capacity Act (MCA) (2005) is designed to empower and protect individuals who possibly lack the mental capacity to decide because the way their brain functions is affected by illness or disability. The MCA provides a legal framework within England and Wales that revolves around acting for and making decisions on behalf of individuals who lack mental capacity. 

Under the MCA, a mental capacity assessment is required before any care or treatment is provided on behalf of the person. 

It should always begin with the assumption that the person has the mental capacity to decide the question. 


Understanding mental capacity in dementia is crucial for respecting individuals' autonomy as their condition progresses. Mental capacity refers to the ability to make decisions and communicate them effectively. In dementia, the loss of mental capacity occurs gradually, impacting various cognitive functions such as memory, communication, and problem-solving. 

Recognizing cognitive changes early, such as memory loss and disorientation, can help identify the need for support in decision-making. Factors influencing mental capacity include biological factors like age and genetics, as well as brain changes such as those caused by dementia or other illnesses. The Mental Capacity Act (MCA) (2005) provides a legal framework for assessing and protecting individuals who may lack mental capacity.


  1. Trachsel M, Hermann H, Biller-Andorno N. Cognitive fluctuations as a challenge for the assessment of decision-making capacity in patients with dementia. Am J Alzheimers Dis Other Demen [Internet]. 2015 Jun [cited 2024 Jan 7];30(4):360–3. Available from: http://journals.sagepub.com/doi/10.1177/1533317514539377
  2. De Sabbata K. Dementia, treatment decisions, and the un convention on the rights of persons with disabilities. A new framework for old problems. Frontiers in Psychiatry [Internet]. 2020 [cited 2024 Jan 7];11. Available from: https://www.frontiersin.org/articles/10.3389/fpsyt.2020.571722
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Catrin Emily Jones

Bachelor of Science - BS, Psychiatric/Mental Health Nurse/Nursing, Swansea University

Cat is a qualified mental health nurse who has worked across multiple sectors, such as hospital wards and in the community. Cat has several years of experience in geriatric nursing, specifically dementia care. She is bilingual and is fluent in both the English and Welsh languages.

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