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Is there a link between dementia and mental illness?

Is there a link between dementia and mental illness?

As anyone who’s ever had any experience with them will probably know, dementia and mental illness – particularly depression – share many of the same symptoms. If, for instance, you were finding it hard to concentrate or had no motivation or any interest in socialising, or if you were having problems with your mood, would you immediately suspect you had depression? Or dementia?
The answer would probably depend on your age, since dementia largely (but not exclusively) affects the older generation. In general though, according to the Mental Health Foundation many people experiencing these types of symptoms may worry they have dementia, when what they actually have is depression (i).
Because some of the symptoms of dementia are often confused for those of depression and other types of mental illness, some of us may wonder whether or not dementia is a mental illness itself. It’s a good question, after all, since both problems affect the brain. The answer isn’t clear cut, however.
For instance, dementia describes a set of symptoms that are caused when the brain is damaged by a disease such as Alzheimer’s disease or a series of strokes (as with vascular dementia). Mental illness also has different causes, including problems with brain chemistry – though recent research suggests that, despite widespread acceptance of the idea, there’s no clear evidence that changes in serotonin levels or activity lead to depression (ii).
Meanwhile, brain damage is a risk factor for mental illness, but not that caused by a stroke or other illness, rather the type caused by a serious head injury – though traumatic brain injuries can start a process in the brain that may eventually cause dementia too. Then again another major risk factor for mental illness is experiencing stressful life situations, which  – as far as we know – isn’t implicated in the development of dementia.
Read more about different types of dementia, including Alzheimer’s and other aspects of cognitive wellbeing by visiting our cognitive health section.
There’s also lots more information and advice on depression and several other mental illnesses in our mental health section


Is dementia classed as a mental illness? 

In the UK dementia isn’t classed as a mental illness. But elsewhere things aren’t that straightforward.
For instance, the gold standard text book for categorising and understanding mental illness is the Diagnostic and Statistical Manual of Mental Disorders, which is produced by the American Psychiatric Association. The fifth edition of this publication (DSM-5) lists dementia in the neurocognitive disorder category. Some would argue, however, that including dementia in DSM-5 in the first place implies it is, in fact, a mental illness.
The answer to the question, ‘Is dementia a mental illness?’ is indeed the subject of much debate. Perhaps it would be more helpful if we asked a different question, such as ‘How are dementia and mental illnesses such as depression linked?’ and ‘Does mental illness raise your risk of developing dementia later in life?’

What is the link between dementia and depression?

According to the Alzheimer’s Society at least one in five people in the UK will experience depression at some point in their lives (iii) – in fact depression mixed with anxiety is currently the most common mental disorder in Britain (iv). Among people with dementia, however, depression is even more common, especially in those with vascular dementia or another type of dementia called Parkinson’s disease dementia.
The US-based Alzheimer’s Association says experts estimate up to 40 percent of people with Alzheimer’s disease suffer from significant depression (v). Similarly, researchers writing in the medical journal Australian Prescriber claim that sustained and disabling depressive episodes are more common in older people with dementia than those of the same age without dementia (vi). They also found that:

  • 30 percent of people with vascular dementia and Alzheimer’s disease are affected by major depression

  • 40 percent with dementia associated with Parkinson’s and Huntingdon’s diseases experience major depression

Depression can affect people with dementia at any stage, but it’s thought to be most common during the early and middle stages of the disease. According to the Alzheimer’s Society, depression can come and go in people with dementia too (iii).
As to why this happens, there are a few factors that may explain why depression and dementia are linked. If someone who’s in the early stages of dementia is also diagnosed with depression, it could well be a direct result of them worrying about their future and how having problems with their memory or other declining abilities might affect them. Alzheimer’s Society experts explain that the diseases that cause dementia can sometimes cause depression too (iii).
Other things that may contribute to depression in someone living with dementia include medication side effects, social isolation, physical illness, lack of energy and an inability to cope with overstimulating situations such as loud and crowded environments.


Differences between dementia and depression

There are, however, a few key differences between dementia and depression:

  1. Most types of dementia tend to develop gradually, often over one or more years. Depression, on the other hand, usually starts more quickly, usually within weeks or a month or two.

  2. People experiencing depression rarely have problems with speech and language, or with knowing where they are or what day or time it is. These things are common in many people with dementia.

  3. Memory problems are common in both dementia and depression. However there are some significant differences. Someone with severe depression may develop memory issues because their concentration isn’t as good as it should be. But if someone prompts them, they will usually remember what they’ve forgotten. Their forgetfulness will also usually improve when their depression lifts. For people with dementia, memory loss doesn’t improve.


How to spot depression in dementia patients

If someone with dementia also has depression it can make their dementia symptoms worse, particularly those that involve thinking and memory. Getting the problem diagnosed as early as possible can lead to treatment and support. So if you live with or care for someone who has dementia, here are some of the signs you should look out for that suggest they may also be suffering from depression:

  • Feeling sad and in low spirits, feeling worthless

  • Worries over health

  • Increased confusion

  • Disturbed sleep

  • Poor appetite

  • Lack of interest in things they used to enjoy

  • Feeling unusually emotional, tearful, restless or angry


Do mental health problems lead to dementia?

Experts from the Alzheimer’s Society say that if someone has had depression in the past, they’re more likely to experience it again if they develop dementia (iii). But if you have experienced depression or other mental health problems earlier in your life, does it mean that you’re more likely to develop dementia when you’re older?
In 2020, experts writing in the medical journal The Lancet published a list of 12 modifiable factors – that is, factors that you can do something about – that increase the risk for dementia (together, they claim, these risk factors account for around 40 percent of dementias worldwide) (vii). The factors include depression along with less education, high blood pressure, hearing difficulties, smoking, obesity, physical inactivity, diabetes, lack of social contact, excessive alcohol consumption, air pollution and traumatic brain injury.
A study carried out by US and New Zealand researchers has since discovered a strong association between mental health conditions and dementia in later life (viii). The study – which involved around 1.7 million people – didn’t try to prove that having a mental illness could cause dementia when you’re older, but it did find significant links between the two.
During the 30 years covered by the study, more than six percent of people with mental health conditions developed Alzheimer’s disease and other types of dementia. Of those who didn’t have a mental health condition, just 1.8 percent developed dementia.
However, it’s important to note that the results of this study do not mean that everyone or most people with mental health problems will eventually develop dementia.


Nutritional supplements to support your brain

There are lots of ways to support your mental and cognitive health including having as healthy a lifestyle as possible. For more details, read our articles on mental health and cognitive health. In the meantime, some of the nutritional supplements that may help support your brain and your emotional wellbeing include the following:

Omega-3 fatty acids

Oily fish such as salmon, herring, mackerel and sardines contain omega-3 fatty acids that are widely thought to be good for your brain and cognitive health (ix). These fatty acids can also be found in fish oil supplements, which are ideal for those who don’t like eating fish.

Researchers have also discovered omega-3 fatty acids may help improve the symptoms of depression (x).

These days even vegans, vegetarians and others who don’t want to take fish oil supplements for ethical or other reasons can enjoy omega-3 fatty acids’ benefits, thanks to supplements that contain omega-3s sourced from marine algae.


Lutein is a natural antioxidant compound called a carotenoid that’s found in a range of foods including dark green leafy vegetables, eggs, corn and avocados (read more about it in What Foods Contain Lutein and Zeaxanthin). It’s well known as a substance that benefits vision health, but scientists now also believe it may have an important role in brain development and function (xi).

B Vitamins

The Bs are essential for human health, including cognitive health, with studies suggesting B vitamins may improve cognitive performance as well as slow down cognitive decline (xii). Some researchers also suggest taking B vitamins may help those who are affected by stress (xiii). B vitamins are available as single supplements, but you may find it more convenient to take them together in a good-quality B complex supplement.

Ginkgo Biloba

Frequently recommended by natural health practitioners to help prevent or treat memory problems, ginkgo biloba may also help increase cognitive function in older people as well as to help delay the progression of Alzheimer’s disease (xiv).

Vitamin D

Vitamin D is probably best known as a supplement for bone health, but more recently it has been linked to other conditions including cardiovascular disease, diabetes and stroke, as well as cognitive problems including dementia. Researchers, for instance, have found that having low vitamin D levels can increase your risk for cognitive decline (xv). Scientists also suspect vitamin D deficiency may be linked to depression because of the way it reduces the buffering of calcium in the brain (xvi).
Vitamin D deficiency is common, however, including in the UK, and Public Health England advises adults and children over the age of one year old to consider taking a daily supplement containing 10mcg of vitamin D, particularly during autumn and winter (xvii).
However if your skin is rarely exposed to the sun – if you spend most of your time indoors, for instance, or if your skin is always covered when you’re out and about – you may need to take vitamin D throughout the year. People with dark skin from African, Afro-Caribbean and South Asian backgrounds may want to consider taking vitamin D all year round too.

The recommended form of vitamin D is vitamin D3 or cholecalciferol, as it’s the natural form of vitamin D the body makes when it’s exposed to sunlight. Vitamin D3 supplements are available in tablet form, and now you can get them in veggie-friendly drops too. However most vitamin D3 supplements are made from the fat of lamb’s wool, which means they’re unsuitable for vegans. The good news is that vegan vitamin D3 supplements sourced from lichen are now more widely available.

Vitamin C

Needed for a variety of essential functions in the body, vitamin C is widely available in supplements (including multivitamins and other combination formulations). There is some evidence that having low levels of vitamin C may be linked with low cognitive performance (xviii), which suggests it may play a part in brain functioning too.


Known best as a curry spice, turmeric contains an active ingredient called curcumin, which is thought to have beneficial effects for certain aspects of cognitive health. Indeed, scientists suggest curcumin may have properties that could help prevent or improve processes underlying age-related cognitive decline and dementia (xix). You’d have to eat a lot of curry to get the amount of curcumin needed for a therapeutic benefit – but thankfully high-strength turmeric/curcumin supplements are now widely available.

The debate about whether or not dementia is a mental illness will probably continue for years, decades even. What we can say is that there do seem to be strong links between some mental illnesses – depression, for instance – and dementia, including the risk for dementia. The good news is that living a healthy lifestyle, which may include taking brain-supporting supplements, could help keep your cognitive and emotional health ticking over nicely. To find out more about lots of different health conditions, take a look around our pharmacy health library.



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Disclaimer: The information presented by Nature's Best is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications.

Our Author - Christine Morgan


Christine Morgan has been a freelance health and wellbeing journalist for almost 20 years, having written for numerous publications including the Daily Mirror, S Magazine, Top Sante, Healthy, Woman & Home, Zest, Allergy, Healthy Times and Pregnancy & Birth; she has also edited several titles such as Women’ Health, Shine’s Real Health & Beauty and All About Health.

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