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13 Jun 2024

The three D’s of the ageing brain: Dementia, Depression, Delirium


The three D’s is a common expression in health of older people.  Standing for Dementia, Depression, and Delirium. These are all separate conditions, they can co-exist in any combination, an older person can have all three conditions at a single time.
Delirium is possibly the least talked about condition. Delirium in older people can be a serious and rapidly progressing condition, it requires prompt medical attention


What is Dementia?

Dementia is an umbrella term for a collection of brain conditions that affect thinking, problem solving, decision-making, behaviour, emotion, and memory, (more than 400 different types of Dementia are known, currently Alzheimer’s is the most common type of Dementia).  People with Dementia can also experience anxiety, Depression, paranoia, Delirium, and a wide range of other conditions.

Dementia generally develops slowly over several years, once deterioration steps up the decline is also usually gradual, over months and years. The executive functions of daily living generally are affected first, (e.g., the functions that require planning and making decisions such as paying bills, food shopping, etc); then the personal care functions of daily living become affected (e.g., cooking, remembering to eat, showering, toileting, etc).  

Commonly the changes include any one or more of the following (this is not a complete list): increasingly giving less thought to matters; deteriorating poor judgement; increasingly it is hard to ‘find’ common words, resulting in disjointed conversation; previous memory may become significantly impaired; may wander with no sense of intent or regard for their personal or others safety; they may shadow (follow closely behind) their key family/whānau carer; get out of bed in the night and be active inside the house (e.g. trying to cook, turning on lights /TV; making a lot of noise; etc). People with high intelligence can mask these factors for a long period of time, but those closest to them may notice distinct changes in their patterns and behaviours.  

Dementia has a significant impact on individuals, families, and communities. People with dementia and their key family/whānau carer may experience the effects of stigma and social ‘demotion’ – not being treated the same way by people. Effects on health, financial circumstances, employment status and relationships with those around them may also have a negative impact on self-esteem.

Who develops Dementia?

In any country around the world, most people with Dementia live in the community, and most are undiagnosed. Currently the cause of Dementia has not been discovered, in some cases it runs in families but that is not the majority of cases. Research to find the cause of Dementia is happening across the world, including the New Zealand Brain Research Centre (for more information https://www.brainresearch.co.nz).

Alzheimer’s Disease International (ADI) is the global voice about Dementia. On 31 July 2020 ADI published in the prestigious Lancet Medical Journal, a list of 12 modifiable risk factors which increasingly evidence is showing if these are ‘corrected’ may prevent or delay up to 40% of Dementia cases globally, to date no priority order of risk has been proven.   

The 12 Modifiable Risks of Dementia  

Physical inactivity


Excessive alcohol consumption

Air pollution

Head injury

Infrequent social contact

Less education


Hypertension (high blood pressure)



Hearing impairment

How many people in New Zealand have Dementia? 

A University of Auckland study in 2020 by Dr Etuini Ma’u, a Psychiatrist of Older Adults, estimated 70,000 New Zealanders had Dementia, that is projected to rise to 100,000 by 2030, and to 170,000 by 2050.

People with Dementia and their families/whānau face significant financial impact from the cost of health and social care, and from the reduction of income. The study conducted by Dr Ma’u showed the economic cost of Dementia to New Zealand increased by 75% between 2011 and 2016, with the total cost estimated as $2.4b in 2016, increasing to $6b by 2050.

Professor Lynette Tippett (New Zealand Brain Research Centre) says “if the onset of Dementia could be delayed by five years, then by 2050 the prevalence of the disease would be lowered by 50%.”


What is Depression?

Depression researchers now say there isn’t much evidence to support the previous claim that Depression results simply from a chemical imbalance in the brain. Clinical Psychologist Dr Jacqui Maguire says, “one prevalent misconception is that Depression is merely a phase, or a sign of personal weakness, when in reality, it’s a complex mental health disorder influenced by various factors beyond an individuals’ control.”   

Different types of Depression exist, with a wide range of symptoms. Generally, Depression does not result from a single event, but from a mix of events and factors. Besides the more common symptoms of sadness; a loss of interest in doing and/or enjoying their normal activities; people can also experience having too much or too little sleep; eating too much or too little; being easily distracted; interference in memory; and lack of focus. The person may also experience feelings of helplessness; irritability; guilt; or they may feel numb, not feeling anything at all; may have suicidal thoughts; and many other symptoms too.

If the older person has a long history of Depression the onset of a new episode of Depression may progressively happen over weeks to months. Late onset Depression is the first episode of depression happening at any age from 65+ years onward; or after several years of no depression an episode of depression happens at any age from 65+ years onward.  

Late onset Depression can have an abrupt onset, but generally that rate of onset is associated with life changes; the symptoms are like those noted above. Changes in sleep patterns are common in late onset Depression, as is short term memory being affected (memory of recent happenings).

More than 50% of the people who develop late onset Depression have never previously had Depression. It may be associated with age-related factors such as other medical conditions, declining physical health, cognitive changes (thinking, memory, emotional and behavioural changes), and structural changes in the brain. Also, psychological and social factors can be closely associated with late onset Depression, such as: retirement from paid work and the resulting changes in life; reduced participation in enjoyable physical or social activities; death of a partner; or admission to 24/7 Age Residential Care.

Who develops Depression? 

The diagnosis of Depression (clinical Depression) is not simply a case of ‘feeling a bit down’ during a rough patch in life, and nor is it the same as anxiety, which is a separate distinct condition, (Note: someone with Depression can also have anxiety and vice versa but they are separate conditions). Clinical Psychologist Dr Dougal Sutherland says developing Depression results from the “combination of nature and nurture, being the genetic predisposition, and the brain structure and functions we are born with, and what we are exposed to in life”.

Thus, treatments for Depression now focus not solely on how you feel, but also on how you think, and what your body requires to function well. Thus, combinations of treatments now commonly include:

  • a short course of medication (to address the overwhelming feelings of sadness etc), combined with
  • lifestyle changes such as: exercise programmes, improving diet, cutting back on alcohol and other drugs, enjoyable self-care measures, social support networks; and
  • learning techniques to change unhelpful ways of thinking, feeling and behaving, such as cognitive behavioural therapy (CBT) and/or personal counselling such as psychotherapy.

Depression in older years can ‘look like’ Dementia, Delirium and other disorders, thus it is important to seek medical diagnosis so as to eliminate a range of other age-related conditions. Accordingly, the treatment options may be different than for mid-life and younger adults with Depression. It is important to go to a doctor as soon as possible when changes in your mood, thinking, memory, or behaviour appear, so that diagnosis and treatment can get underway promptly to enable as good a quality of life as possible across the ageing journey. For more information https://mentalhealth.org.nz/resources/resource/Depression-in-later-life

How many older people in New Zealand have Depression?

It is estimated that as many as one in six New Zealanders will experience a major depressive episode at some point in their life. The last national prevalence study of Depression in New Zealand was two decades ago hence there is no current complete ‘picture’.   

However, the Mental Health Foundation of New Zealand advises that data of diagnosed cases of Depression tell us that adult male rates have increased from 15% in 2012 to around 25% today, and from 10% to 12% for adult women during the same period. Multiple public awareness campaigns since 2012 have made it easier for men to seek assistance for symptoms of Depression. Experts, however, consider that is not the full answer for the substantial increase in male rates of diagnosed Depression.

Older people are defined in Aotearoa New Zealand as those 65+ years old.

A New Zealand study by Doctors Grace Pearson and Ngaire Kerse, et al (2019) states “New Zealand has an ageing population with people of 85 years plus projected to quadruple in size by 2068. They also state, “over 20% of older adults suffer from a neuropsychiatric disorder, of which Depression is the most common. Later-life Depression is independently associated with a 41% increased risk of death (from all causes), and it is the leading cause of disability worldwide. With such an impact on physical health, it is unsurprising therefore, that Depression in older people doubles hospitalisation rates and length of stay thereof.”           



What is Delirium?

Delirium is frequently mistaken as a change in a person’s pre-existing Dementia and/or Depression, or the onset of either of these conditions. The symptoms of Delirium can be similar to those of Dementia or Depression. Generally, the telltale difference for Delirium is the changes happen suddenly, within hours or days.

Common causes of delirium in older people include major changes such as: shifting house; intoxication/overdose or withdrawal from alcohol and/or drugs; a sudden shock to their  system such as a fall, with or without injury; pain; fatigue; constipation; dehydration from diarrhoea, and/or vomiting, or for other reasons; reactions to medication; infections in the lungs, blood, especially urinary tract infections (UTI), or other infections; pre-existing conditions that become unstable (e.g. diabetes, cancers, Dementia, heart conditions, kidney conditions; etc); following a stroke; or multiple other reasons. In short ‘things’ that disrupt an older person’s established equilibrium can trigger Delirium.

Delirium is a medical illness, if recognised at an early stage, with a well-managed treatment plan promptly commenced, the expectation is the older person should return to their previous level of cognition and functioning.           

What are the symptoms of Delirium?

Onset is usually sudden; the changes are obvious generally within hours or days of the cause happening. Like Dementia and Depression, Delirium also affects brain functions.

Delirium usually includes fluctuating changes in the person’s mental state, swinging from being quiet and vague; through to being loud, antagonistic and aggressive; followed by periods where they appear similar to their previous mental state.

For example, someone who was previously quiet and non-violent can within a short period of time start shouting and hitting out; or vice versa. They can display all or some of the following: overly alert, ‘busy’ and moving a lot, agitated, aggressive, quiet, inattentive, drowsy, disorganised thinking, hallucinations, and wide mood changes. However, some people with Delirium may within hours or days start drifting in and out of consciousness and have no loud or aggressive outbursts.

Delirium usually responds to correct treatment. For most the symptoms may markedly improve within around six – ten days of an appropriate treatment plan commencing. Others, their symptoms may take much longer to clear after an appropriate treatment plan commences. A small number may still have Delirium more than a month after an appropriate treatment plan commenced.          

It is important to know Delirium can progress rapidly, it can cause death. Prompt medical attention is essential for older people who within hours or a few days exhibit marked changes in their usual mood, behaviours, ways of being; don’t think it is due to changes in their Dementia or Depression.  

How to interact with someone with Delirium?

Create a supportive calm environment, with minimal change of routine, don’t over stimulate the person with noise and activity. When they are conscious, ensure they drink plenty of non-alcohol fluids and eat small frequent amounts of nourishing food, and that they take all prescribed medications – especially any medications for infections.   

When communicating with someone with/recovering from Delirium:  

  • Stay calm.
  • Talk to them in short, simple sentences, with only one point in each sentence.
  • Repeat things if necessary and always in a calm voice.
  • Reassure them what is happening, encourage that recovery is likely if all the treatment plan steps are followed.
  • Remind them of the date and time – make sure they can see a clock and calendar showing the current time and date.

It may take weeks or months to fully recover from the impact of having Delirium. An older person recovering from Delirium will likely tire more easily, they may need reminding to build some daytime rest into their schedule; and they need to be encouraged to drink plenty of non-alcohol fluids every day for the rest of their life – for more information about what a normal daily fluid intake should be for people 65+ years refer to www.selwynfoundation.org.nz/learning/information-about-ageing/hydration-for-health/


Is it Dementia, Depression, or Delirium?

In summary it can be hard to know, even for health professionals, whether any change in a 65+ year olds usual way of being is due to Dementia, Depression, or Delirium. Trust your judgement, if the person suddenly within hours or a few days seems ‘different’, seek prompt medical attention. Even if the person has recently seen a health professional, but subsequently exhibits a sudden onset of changes, return for prompt medical attention.       

Seeking professional guidance and educating yourself and others about the signs of Depression, Dementia, and Delirium may improve the quality of everyday life for that person, it could save their life if they have Delirium.


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Published:  June 2024

To be reviewed: April 2027