Knitted neurons at Francis Crick Institute exhibition, Hello Brain. January 2025
What's in a word?
Dementia is a generic term for several diseases that affect memory, thinking and the ability to perform daily activities, and is more common among women than men. But what a word! Isn’t it about time we came up with a less stigmatising term for diseases of the brain that predominantly affect older people?
But in the meantime, here is some useful information.
Alzheimer’s Disease (AD) is the most common of these diseases and accounts for up to 70% of cases. Other common diseases are vascular dementia (VD), frontal lobe dementia (FLD) and Lewy body disease (LBD). While the diseases are all different, they result in similar disabilities. The boundaries between different forms of dementia can be indistinct, particularly in people over the age of 65 years. Mixed forms often co-exist.
In 2021 there were 57 million people living with dementia worldwide, although this may well be an underestimate, as many are undiagnosed. Dementia is currently the seventh leading cause of death and a major cause of disability and dependency among older people. In 2019, dementia cost the world’s economy 1.3 trillion US dollars. A significant proportion of this is the estimated cost of informal care, predominantly provided by women.
While numbers of people living with dementia are increasing (due to increasing longevity) there is evidence that the rate of dementia in high-income countries is declining. A systematic review provided by The Lancet Standing Commission on dementia (2024) suggested that rates of dementia are decreasing in these countries as a result of changes such as compulsory education and reduced smoking.
Warning signs
There is a tendency among us older people to regard every mental slip as a definite sign of dementia, but it is important not to panic. Forgetting your keys or looking for your glasses when they are on your head are not diagnostic!
In the previous post we looked at normal brain ageing and cognitive decline. Here are some of the warning signs of dementia:
*Difficulty remembering the names of family or close friends, or recognising them;
*Endless repetition of the same questions;
*Getting lost in familiar places;
*Struggling to complete routine tasks; and
*Mood changes (although there are other common causes for this).
Risk factors for dementia
While certain genes (e.g. APOE- ε4 gene) are associated with an increased risk of dementia, having dementia in your ancestry does not mean you will inevitably get the disease.
The main risk factor for dementia is age: around 2% percent of people between 65 and 69 years of age have dementia, and the risk doubles roughly every five years. This means that around a third of people over the age of 90 years have dementia. Young onset dementia, (ie under 65 years), is relatively uncommon and is thought to account for between 2% and 8% of all dementia.
Certain health conditions can increase the risk of developing dementia. These include high blood pressure (hypertension), high blood sugar (diabetes), high cholesterol, heart disease, strokes and Parkinson’s disease. Down’s syndrome and other learning disorders can significantly increase the risk of developing dementia in later life. Cardiovascular risk factors are especially linked to the risk of developing vascular dementia.
As seen in the previous post education, or lack thereof, is implicated in dementia. The Lancet review lists poor education as one of 14 risk factors for dementia. One study showed that differences in the quality of education, as measured by reading levels at ages 14-15 years, have been estimated to account for about half the US disparities in dementia prevalence across racial groups. Other studies that include participants from high- income countries, Asia and China show similar patterns.
Geriatricians believe that some 40% of all dementia is preventable because many of the risk factors are modifiable. This means by making changes in our lives, we can reduce the risk of dementia.
Some potentially modifiable factors include:
*Smoking: Smoking is a clearly recognised risk factor for vascular disease and cancer. It is less well known that it is a significant risk factor for AD and other dementias. The World Health Organisation estimates that 14% of cases of dementia worldwide could be caused by smoking. Smoking causes oxidative stress and directly harms blood vessels. Studies suggest that stopping smoking reduces this risk substantially. A review of 37 research studies found that compared to people who had never smoked, current smokers were 30% more likely to develop dementia in general, and 40% more likely to develop Alzheimer’s Disease. The risks were higher the more they smoked.
*Air pollution: Smoke particles from traffic fumes and burning wood in homes increases the risk of dementia, probably from damage to blood vessels. The Lancet review reports a large number of studies in high-, and low-middle- income countries showing that high and increasing levels of particulate matter in the air are associated with Alzheimer’s Disease.
*Excessive drinking: Again, The Lancet review quotes many studies across the globe that show a relationship between heavy drinking and dementia. Chronic heavy drinking may lead to permanent damage to the brain. Healthy drinking is less than 14 units per week. As alcohol is now much stronger and we may not know the volume of our glasses, people often underestimate the amount they are drinking.
*Obesity: This leads to metabolic changes and increased risk of cardiovascular disease and dementia. Studies have shown that obesity in mid-life (35-65) can increase dementia risk by about 30%. Being overweight, but not obese, does not carry the same risk.
*Sedentary lifestyle: The Alzheimer’s Society estimates that a sedentary lifestyle contributes around 2% of dementia cases worldwide. Research has found that a year of regular physical activity can make the memory centres in our brain larger.
*Diet: A systematic review in 2023 (38 studies) showed that the typical western diet is a risk factor for developing AD. Consumption of refined carbohydrates and diets with a high glycaemic index (available sugar) are associated with changes in the brain typical of people with AD. Ultra-processed foods (UPF) are particular culprits. UPFs cause weight gain and affect our blood sugars and fats (metabolic syndrome). This increases our risk of heart disease, high blood pressure and strokes, and leads to changes in the blood supply of the brain. Such changes certainly increase the risk of vascular dementia and may well increase the risk of AD too. A recent study showed that people who consumed UPFs were more likely to develop dementia (both AD and VD). Furthermore, by replacing 10% of UPF by weight in the diet with an equivalent proportion of unprocessed or minimally processed foods was estimated to be associated with a 19% lower risk of dementia. Improved diet can reverse some of the metabolic changes, for example improving blood sugar control, and therefore may have some effect on improving brain function, although not reversing damage.
*Depression: Having episodes of depression increases the risk of developing dementia. The Lancet review covers seven studies which show this link. New depression later in life may however represent early dementia.
*Traumatic brain injury: Much has been written about the relationships between recurrent small injuries and dementia in contact sports such as boxing and rugby, but a severe single head injury may also pose a risk. Overall, the evidence suggests that brain injury may lead to earlier onset of dementia by 2-3 years. In terms of sports, it is important to note that the risk is predominantly in professional players and should be balanced against the health benefits of taking exercise.
*Untreated hearing loss: Hearing loss between the ages of 40-65 years increases the risk of dementia by an estimated 7%. This is thought to be both from the effects of withdrawing from social interaction as well as depriving the brain of neurological stimulation.
*Social isolation: Based on current research, the Alzheimer’s Society estimates that almost half of dementia cases worldwide can be prevented or delayed if everyone kept socially connected. This is borne out by a wide range of studies discussed in The Lancet review.
*Untreated vision loss: The link between untreated vision loss and dementia has emerged from recent research. One study showed that people with untreated cataracts and diabetic retinopathy had a higher risk of dementia, but not those with age-related macular degeneration or glaucoma.
The Lancet review also discusses additional risk factors, which have not been conclusively proven:
*Sleep: Various studies have shown a U-shaped association between sleep and dementia with less than seven hours a night, and more than ten being equally risky. However other studies contradict this, suggesting that it is the quality of sleep that is more important.
*Post-traumatic stress disorder (PTSD): Three studies in USA, Denmark and Taiwan observed an increased risk of dementia in people who experienced PTSD. However, one follow-up study over five years suggested that the increased risk of dementia was from other causes.
Medical interventions
Health professionals are able to assess some of the risks of dementia among their patients and provide treatment to prevent or delay its development. For example:
*Blood pressure medication. There is data to suggest that blood pressure medications may reduce the chances of developing dementia. For example one study (the SPRINT MIND trial) showed that patients whose high blood pressure (BP) was treated intensively to reduce their systolic BP (upper figure) to 120 mmHg showed a significantly lower incidence of mild cognitive decline and dementia than those on standard treatment (to lower BP to lower than 140 mmHg). Other trials have been conflicting, with some suggesting blood pressure control is helpful and others not. However good blood pressure control reduces heart attacks and strokes so is important.
*Cholesterol medication (statins). There have been a number of studies looking at evidence for an association between statin use and dementia risk. A recent meta-analysis of 30 studies involved over nine million people, of whom 84,101 were dementia patients. They found that statin use was associated with a 17% decreased risk of all-caused dementia with a significantly decreased risk of AD, although surprisingly no effect on VD.
*Sedative medication. There have been a number of trials looking at the relationship between chronic use of sedative drugs such as anti-depressants, anti-psychotics and sleeping tablets (benzodiazepines), and dementia. Although several trials have shown that these drugs, in particular the benzodiazepines, can increase the risk of dementia, it is not clear that there is a causal relationship. What is clear is that in patients with early memory problems, sedatives can make the memory worse. Although if being used for anxiety, paradoxically they may help by reducing the anxiety that affects memory.
*Shingles vaccine: A recent study has shown that older people who had the shingles vaccine were significantly less likely to develop dementia in the next six years than those who did not have the vaccination.
*Acid reflux medication: New research suggests a strong association between long term use of proton pump inhibitors (PPIs) such as omeprazole, and dementia. People who had used the drugs for more than 4.4 years were at 33% higher risk of developing dementia. Other studies have refuted this, but more research is needed to understand the impact of this very commonly prescribed medication.
This diagram (below) from The Lancet review summarises possible mechanisms for maintaining cognitive reserve and reducing dementia risk.
There is a huge amount of research that shows how we can protect ourselves from getting dementia as we age. In the previous post we looked at simple ways to prevent or delay diseases of the brain. In future posts we will examine a range of interventions and strategies for healthy ageing of the body and the mind.
References
*Livingstone G et al. Dementia Prevention and Care:2024 report of The Lancet Standing Commission on dementia. Published online July 31, 2024 https://doi.org/10.1016/S0140-6736(24)01296-0
*World Health Organization. Dementia: Key facts, March 2025. https://www.who.int/news-room/fact-sheets/detail/dementia
*Makadam N. Changes in prevalence and incidence of dementia and risk factors for dementia: an analysis from cohort studies. The Lancet Public Health, Volume 9, Issue 7, 2024. Link
*ASH: The link between smoking and dementia. Link.
*Alzheimer’s Society: Physical activity and dementia risk. Link
*Alzheimer’s Society: Obesity and dementia risk.https://www.alzheimers.org.uk/about-dementia/managing-the-risk-of-dementia/reduce-your-risk-of-dementia/obesity - :~:text=Does obesity increase the risk,which contribute to dementia risk
*Lou et al. Effect of nutrition in Alzheimer’s Disease” A systematic review 2023. Neurosci., 04 May 2023. Volume 17 - 2023 | https://doi.org/10.3389/fnins.2023.1147177
*Age UK. Diet and brain health. Link
*Li et al. Association of Ultra-processed Food Consumption With Risk of Dementia: A Prospective Cohort Study. Neurology. 2022 Sep 6;99(10): e1056-e1066. doi: 10.1212/WNL.0000000000200871. Epub 2022 Jul 27. PMID: 36219796.
*Jiang C, et al. Diastolic Blood Pressure and Intensive Blood Pressure Control on Cognitive Outcomes: Insights from the SPRINT MIND Trial. Hypertension, 2023. Link.
*Poly TN et al, Association between Use of Statin and Risk of Dementia: A Meta-Analysis of MC,
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*Bodmer I, et al. Benzodiazepine Use and Risk of Developing Alzheimer’s Disease or Vascular Dementia: A Case–Control Analysis. Drug Safety. 2015;38(10):909–19] Link
*Taquet M, et al The recombinant shingles vaccine is associated with lower risk of dementia. Nat Med 30, 2777–2781 (2024). Link
*Northuis C et al, Cumulative Use of Proton Pump Inhibitors and Risk of Dementia
Neurology October 31, 2023 issue 101 (18) Link