The most common types of dementia – Alzheimer’s disease, vascular dementia, dementia with Lewy bodies and frontotemporal dementia – are all progressive.

This means that the structure and chemistry of the brain become increasingly damaged over time. The person’s ability to remember, understand, reason and communicate will gradually decline.

As dementia worsens, the person will need more and more support with daily living. Their behaviour and mood will also change.

How is dementia measured?

Health professionals often use scales to measure these changes. At different times they may assess a person’s mental ability (eg Mini Mental State Examination), daily living skills (eg dressing, managing medication), behaviours, overall functioning or quality of life.

Some of these scales were developed specifically for Alzheimer’s disease and work better for that than for other types of dementia. Assessment of the extent of someone’s dementia should take account of these scales but should also take a broader view of the person, including their capabilities and needs.

Each person experiences dementia in their own way. However, looking at dementia as a series of three stages – early, middle and late – can be a useful way of understanding the changes that occur over time.

This is because:

• some symptoms may appear earlier or later than indicated here, in a different order, or not at all
• the stages may overlap – the person may need help with one task, but may be able to manage another activity on their own
• some symptoms, such as irritability, may appear at one stage and then vanish, while others, such as memory loss, will worsen over time.

The way that a person experiences dementia will depend on many factors. These include their physical make-up, other illnesses they may have, their emotional resilience, the medication they take and the support they can rely on.

While it can be helpful for planning ahead to have some awareness of the likely progression of a person’s dementia, it is important to realise that everyone’s experience will be different.

It is much more important to focus on trying to live well with dementia, meeting the needs of the person at that time, than to focus only on which stage they are in.

Before dementia develops

There is good evidence that, by the time most people develop any symptoms of dementia, the underlying disease has been causing damage to their brain for years.

Researchers are very interested in this ‘pre-symptomatic’ period and have developed tests to look at the brain chemistry, function and structure at this time. It is likely that any medication designed to slow down or prevent the diseases that cause dementia would work in this early phase, before the disease is fully established.

Over time, the changes in the brain will begin to cause mild symptoms, but which are initially not bad enough to count as dementia. Subtle problems in areas such as memory, reasoning, planning or judgement may cause difficulties with more demanding tasks (eg preparing a meal) but they will not yet significantly affect daily life.

A person at this stage may be given a diagnosis of mild cognitive impairment (MCI). About 10–15 per cent of people with this diagnosis will go on to develop dementia each year.

Rate of progression

The speed at which dementia worsens varies widely. There are some differences between the different dementias – Alzheimer’s disease, for example, seems to have the slowest progression on average – but much of the variation is from person to person.

A wide range of factors influence how quickly someone’s dementia will progress. These include age – people who develop symptoms before 65 often have a faster progression.

Evidence also suggests that a person’s genes play a role, as does someone’s overall physical health. People with poorly controlled heart conditions or diabetes, those who have had several strokes or those who have repeated infections are all likely to have a faster deterioration.

On the positive side, there is some evidence that keeping active and involved can help a person with dementia retain abilities for longer. Regular physical exercise in particular seems to slow the rate of decline.

Some of these factors affect the underlying disease processes in the brain, while others do not but still help with dementia symptoms.

Those supporting someone with dementia should help them to stay active – physically, mentally and socially. The person with dementia should also try to eat healthily, get enough sleep, take medications as advised and not smoke or drink too much alcohol.

It is also important for the person to have regular check-ups (for eyes, ears, teeth and feet) and vaccinations, and to keep a careful eye on underlying health conditions. A sudden change in the person’s abilities or behaviour could indicate a physical or psychological health problem or an infection.