Dementia is a serious health challenge in Australasia and globally, so it is worth examining how it might be prevented.

Dementia statistics

• Worldwide, 50 million people live with dementia.
• It is the second leading cause of death in Australia and the leading cause of death for women.
• It affects 30% more women than men.
• It is estimated that 472,000 Australians and almost 70,000 New Zealanders live with dementia, and this number is set to more than double by 2050 due to aging populations.
• The cost of dementia in Australia in 2018 was AU$15 billion and is around and NZ$1.7 billion in New Zealand.

What is dementia?

Dementia is an umbrella term that describes symptoms that are caused by disorders of the brain. There are many kinds of dementia and Alzheimer’s disease is the most common. Dementia is progressive and gets worse over time.

Risk factor and prevention

Like so many other chronic diseases, lifestyle is important. Alzheimer’s New Zealand says keeping active, eating healthily and staying mentally active and social can all reduce the risk. They’ve developed an infographic to help educate the public (see image above). The evidence behind this advice is summarised in a report published in 2020 by the Lancet Commission: Dementia prevention, intervention, and care (Livingston 2020). The report identified 12 risk factors that if addressed could prevent or delay up to 40 per cent of dementias worldwide. Many are common to other chronic diseases. Three new risk factors have been identified since the last Lancet Commission report on preventing dementia in 2017: excessive alcohol consumption, traumatic brain injury and air pollution.

The 12 risk factors accounting for 40% dementia globally

1. Less education in early life

Higher lifelong education attainment reduces risk, but cognitive stimulation in early life is important. Having lower levels of education before the age of 45 results in lower ‘cognitive reserve’. Policy to support early childhood education for all would be an effective public health measure.

2. Hearing loss

Hearing loss reduces cognition, even at the subclinical level (at which treatment is not indicated) and this may result in cognitive decline. Using hearing aids appears to reduce the risk from hearing loss.

3. Smoking

Stopping smoking, even in later life, reduces the risk. Second-hand smoke exposure may also pose a risk but evidence is scarce.

4. High blood pressure

Persistent midlife hypertension is associated with an increased risk of dementia in late life. Treatment to maintain systolic blood pressure to 130mm Hg or less from around age 40 is recommended. Until very recently (see stop press below), the only known effective treatment medications for dementia are anti-hypertensives.

5. Obesity

Higher body mass is associated with increased dementia risk, and the risk is greatest in obesity (BMI >30).

6. Depression.

Depression is an early onset symptom of dementia, and may have a bidirectional impact (dementia may also cause depression). Antidepressants do not appear to reduce dementia risk but more research is needed.

7. Physical inactivity

There is convincing evidence for physical activity protecting against dementia. Sustained exercise in midlife, and possibly later life, is protective.

8. Diabetes

Type 2 diabetes is a risk factor for dementia. Intensive blood glucose control does not appear to decrease risk.

9. Infrequent social contact

Frequent social contact enhances cognitive reserve and encourages protective behaviours. Being single in late life appears to reduce social contact.

10. Excessive alcohol consumption

Misusing alcohol and drinking more than 21 units weekly (equivalent to 17 standard drinks in Australia and New Zealand) increases risk. The relationship is complex as studies have shown reduced risk with light-moderate drinking (less than 14 units [11 ANZ standard drinks]) and increased risk from abstinence.

11. Head injury

Traumatic Brain Injury (TBI) such as fracture, concussion, oedema and brain bleed increase risk, including sports head injury.

12. Air pollution.

High nitrogen dioxide and fine ambient particulate matter from vehicle exhaust and wood burning are associated with increased dementia risk. Particulates in the air have toxic vascular effects like smoking and may accelerate neurodegeneration.

STOP PRESS

On the 7th June the USA Food and Drug Administration (FDA) approved a new drug for the treatment of Alzheimer’s Disease called aducanumab (Aduhelm™), via an accelerated approval pathway. Aducanumab is a novel therapy consisting of antibodies that target amyloid beta plaques in the brain and is the first drug to do this. It may take some time before approval is granted in Australia and New Zealand.

How does prevention work?

There are two major pathways by which preventive activity is thought to protect against dementia: first is by reducing neuropathological damage, either from protein (e.g. amyloid) plaque build-up, vascular damage or inflammation; and second is by increasing and maintaining ‘cognitive reserve’. Cognitive reserve can be explained as an individual’s resistance to symptoms despite neuropathology. Or in other words, having a healthier and more interconnected brain to start with means there is more time after disease onset before symptoms become a problem.

Dietary prevention

A systematic review and meta-analysis of prospective cohort studies with 34,168 participants found a high Mediterranean diet score was inversely associated with the development of cognitive disorders such as dementia (RR 0.79) (Wu 2017). Another review of dietary patterns and the risk of cognitive decline and Alzheimer’s Disease found higher adherence to the Mediterranean Diet and DASH diet (Dietary Approaches to Stop Hypertension) was associated with less cognitive decline, and the strongest associations were observed with the MIND diet (Mediterranean-DASH diet for Neurodegenerative Delay). The MIND diet emphasizes plant-based foods, limited animal foods and foods high in saturated fat and specifies consumption of berries and green leafy vegetables (van den Brink 2019).

Is there any link with dietary sugar?

While improved overall diet quality and healthier dietary patterns such as the Mediterranean diet have been associated with reduced risk of developing dementia in numerous (although not all) studies and systematic reviews, there is little evidence supporting dietary sugars as an independent dietary risk factor.  

REFERENCES

• Dementia Australia. Dementia Statistics.
• Livingston G. et al. (2020). Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. The Lancet Commissions, 396(10248):413-446.
• Alzheimer’s New Zealand. Facts and Figures.
• US FDA . FDA’s Decision to Approve New Treatment for Alzheimer’s Disease.
• van den Brink AC, Brouwer-Brolsma EM, Berendsen AAM, et al. (2019). The mediterranean, dietary approaches to stop hypertension (DASH), and mediterranean-DASH intervention for neurodegenerative delay (MIND) diets are associated with less cognitive decline and a lower risk of alzheimer's disease - a review. Adv Nutr, 10(6):1040-1065.
• Wu L, Sun D. (2017). Adherence to mediterranean diet and risk of developing cognitive disorders: an updated systematic review and meta-analysis of prospective cohort studies. Sci Rep, 7: 41317.