Introduction

Alzheimer's disease is a progressive neurodegenerative disorder characterised by declining cognitive ability. It is recognised as the leading cause of dementia in the ageing population. First described by Alois Alzheimer, a German psychiatrist, in 1906, Alzheimer’s disease is now a global public health concern and a significant cause of mortality. Projections indicate that the prevalence of Alzheimer's and other dementias will reach 139 million worldwide by 2050. So, the urgency for effective prevention and treatment strategies has never been greater.¹ 

Nutrition has become a crucial factor in preventing and managing Alzheimer's disease. While there is currently no cure for Alzheimer's disease, a growing body of research highlights the potential of dietary modifications and nutritional supplements to mitigate the risk and slow the progression of the disease. Understanding the relationship between nutrition and brain health offers a promising avenue for reducing the incidence of Alzheimer's and improving the quality of life for those affected.¹ 

This article explores the vital role of key nutrients, dietary patterns, and specific foods in the context of Alzheimer's disease, providing insights into how we can harness nutrition to combat this pervasive condition.

How do nutritional supplements help?

Nutritional supplements contain health-promoting constituents that support regeneration, slow the ageing process, and combat pathogens responsible for developing Alzheimer’s disease. Compared to expensive treatments and therapies, nutritional interventions are cost-effective, safe, socially acceptable, easy to implement, and typically have fewer side effects.^2,3 

While there is no known cure for Alzheimer's, treatment approaches often focus on maximising the transmission of acetylcholine and other neurotransmitters and other strategies like nutritional compounds. These brain chemicals assist with general brain functions like memory and thinking. As a result, overall well-being is achieved, and the chances of acquiring Alzheimer's disease are reduced.

Key nutrients

Antioxidants

People with Alzheimer's disease experience increased oxidative stress levels.⁴ Antioxidants work wonders, reducing oxidised membrane lipids, preventing protein damage, limiting nucleic acid damage, and influencing certain stress-induced pathways in cells. 

Vitamin A and β-Carotene

These inhibit the formation of both Aβ oligomers and fibrils which have a role in AD and have anti-oligomerisation effects on Aβ. Lower serum and plasma concentrations of vitamin A were seen in Alzheimer patients, and higher β-carotene levels are associated with better memory performance.

Vitamin E and Vitamin C 

Vitamin E, found in wheat germ, sunflower, safflower oil, asparagus, and leafy greens, should be taken with vitamin C, a recharging antioxidant, to maximise its effects. Vitamin C, abundant in citrus fruits and berries, reduces Aβ oligomer formation and oxidative stress.

Selenium

Selenium is an element that protects brain cells from oxidative stress and inflammation. It is vital in antioxidative defence since Alzheimer's patients often show lower selenium levels in plasma, red blood cells, and nails. Selenium detoxifies harmful peroxidases, supports brain health and is useful in Alzheimer's prevention and management. Some of the dietary sources include Brazil nuts, seafood, and cereals.

Polyphenols

Polyphenols are potent berries, tea, coffee, and red wine antioxidants. They may protect brain cells by reducing oxidative stress and inflammation, enhancing neurogenesis, and improving cognitive functions. 

B vitamins (vitamin B12, B6, and folate)

These vitamins are crucial for neuronal health, energy metabolism, and their actions as methyl donors. High serum homocysteine levels and lower vitamin B12 levels are associated with an increased risk of Alzheimer's Disease. Vitamin B6 inhibits oxidative stress, and higher levels of these vitamins lower plasma homocysteine concentration.^5,6

Omega-3 fatty acids

Omega-3 fatty acids, particularly DHA (docosahexaenoic acid), are essential for brain health. They stabilise cell membranes, enhance fluidity, and improve synaptic connectivity. It also affects the expression of genes that might influence inflammatory processes. DHA is found in fatty fish (salmon, mackerel, sardines), flaxseeds, chia seeds, and walnuts.

Carbohydrates

Patients with type 2 diabetes mellitus have an increased risk of Alzheimer's, often showing reduced insulin levels in the brain. A diet rich in complex carbohydrates, such as whole grains, fruits and vegetables, helps maintain steady blood glucose levels and supports brain health. Balancing carbohydrate intake is essential to avoid insulin resistance, which can bring a cognitive decline. 

Curcumin

Curcumin, found in turmeric, is anti-inflammatory and has antioxidant properties. It helps reduce amyloid plaques, characteristic of Alzheimer's, and combats inflammation. Incorporating curcumin into the diet has significant neuroprotective benefits.

Flavonoids

Flavonoids in various fruits, vegetables, tea and dark chocolate help protect against cognitive decline. They improve brain function by enhancing memory and learning and protecting neurons from damage. Regular incorporation of flavonoids in the diet is associated with a lower risk of cognitive decline and dementia, making them a key component of a brain-healthy diet. 

Effects of foods and beverages on Alzheimer’s disease

Nutrients are not consumed in isolation but as part of a diet. Examining food rather than individual nutrients provides a more holistic understanding of their relationship with Alzheimer’s disease.^1,7

Fish

Regular fish consumption reduces the risk of dementia and Alzheimer's. Fish such as salmon, mackerel, sardines, and trout are rich sources of omega-3, particularly DHA and EPA, which are essential for brain health. Studies show that people who consume fish more than once a week have a 60% lower chance of developing the disease.⁸

Fruits and vegetables

Fruits and vegetables are rich sources of antioxidants and bioactive compounds like vitamins E and C, carotenoids, and flavonoids, and low in saturated fats, all of which contribute to brain health and may help reduce the risk of Alzheimer’s disease. Green leafy vegetables, such as spinach, kale, and collards, are high in vitamins K, C and E, as well as folates.

Regular consumption of these vegetables is associated with a slower rate of cognitive decline.¹ Cruciferous vegetables like broccoli, cauliflower and Brussels sprouts are rich in antioxidants, which improve mental functions.

Dairy

Dairy products, rich in vitamin D, phosphorus, and magnesium, decrease the risk of cognitive impairment by reducing vascular alterations and structural brain changes that occur with cognitive decline.¹ However, the consumption of whole-fat dairy products is linked to cognitive decline. Unsaturated fats from dairy products decrease the risk of acquiring Alzheimer's, whereas saturated fat intake increases the risk. 

Coffee and tea

Coffee, a rich source of caffeine, protects against Alzheimer's due to components in coffee that synergise with caffeine to enhance plasma cytokines, proteins that regulate inflammation. Black tea enhances auditory and visual attention, while green tea polyphenols inhibit cognitive impairment by modulating oxidative stress.

Alcohol

Light to moderate alcohol intake is associated with a lower risk of Alzheimer's disease, while heavy consumption and heavy smoking are linked to an earlier onset. Resveratrol and other polyphenols in red wine reduce plaque formation and protect against Aβ-induced neurotoxicity. Due to its bioavailable silicon, moderate beer consumption provides a protective factor for the disease.⁹

Dietary patterns for prevention

Mediterranean diet

People in the Mediterranean region, like Naples and other areas of Italy, have been studied to have the highest life expectancy and the lowest incidences of Alzheimer’s disease. This is attributed to their dietary habits, including ample fruits, vegetables, olive oil, whole grains, beans, nuts, seeds, fish, poultry, and dairy products, with moderate alcohol consumption and limited red meat and sweets.

Greater adherence to the Mediterranean diet is linked to a lower risk of Alzheimer’s due to its anti-inflammatory properties and oxidative stress-induced, regenerative and cellular health processes.¹⁰

Japanese diet

A high consumption of fish, soybeans, seaweed, vegetables, and fruits and a low intake of refined carbohydrates, sugars, and animal fats characterises the Japanese diet. This diet ensures ample intake of vitamins, minerals, and antioxidants, which supports cognitive health.¹¹

DASH diet

The Dietary Approaches to Stop Hypertension (DASH) diet emphasises plant foods, fruits, vegetables, fish, poultry, whole grains, low-fat dairy products, and nuts while minimising red meat, sodium, sweets, and sugar-sweetened beverages. This diet is high in potassium, calcium, magnesium, and fibre, with relatively low sodium and saturated fat content, which help reduce blood pressure and support cardiovascular health. Since hypertension and cardiovascular disease are risk factors for Alzheimer’s disease, the DASH diet indirectly supports brain health by promoting a healthy heart and vascular system.¹² 

Summary

A nutritional approach to preventing Alzheimer's disease is a safe and socially acceptable strategy. While further research is needed to improve the quality of evidence on the associations of different nutrients, foods, and dietary patterns with AD, current findings suggest that dietary modifications and nutritional supplements can play a significant role in reducing the risk and slowing the progression of Alzheimer's disease. Adopting healthy eating habits early in life may be a key strategy in preventing this debilitating condition.