Diets and Chronic Diseases (Part 4: Alzheimer’s Disease)

by | Jan 2, 2019

Diets and Chronic Diseases (Part 4: Alzheimer’s Disease)

Many chronic diseases such as type 2 diabetes; hypertension (high blood pressure); heart disease; age-related cognitive decline including dementia and Alzheimer’s disease; and cancers may be thought of as inevitable part of aging.

Although statistically, the prevalence of these chronic diseases increases with age, especially after age 40, numerous clinical research and studies have shown the strong influence of diets and lifestyle in the prevention and management of these diseases.

Let’s not be part of the statistics!

In Part 4 of this article series, we present a summary of what the latest research have shown in terms of the appropriate diets for the prevention and management of age-related cognitive decline, specifically Alzheimer’s disease (AD), the most common type of dementia.

The identified risk factors and contributors are also presented.

Prevalence

Dementia is a general description of symptoms associated with decline in cognitive and mental functions.1

AD is the most common type of dementia, accounting for 60 to 80% of cases in the United States.1

Vascular dementia, caused by damaged blood vessels in the brain compromising delivery of nutrients and oxygen, is the second most common type of dementia. 1

Other conditions that may contribute to dementia include thyroid problems and vitamin deficiencies.1

AD is the 6th leading cause of death in the United States. 1 in 10 people age 65 and older has AD. An estimated 5.7 million Americans are living with AD in 2018, with 5.5 million being of age 65 and older. About 2/3 of the affected individuals are women.1

Risk Factors and Contributors to AD

AD is a degenerative brain disease with two major hallmarks of brain structure abnormalities, i.e., amyloid plaques and neurofibrillary tangles (NFTs).

Both amyloid plaques and NFTs lead to loss of communication between neurons, as well as damage and eventual death of neurons, affecting the parts of the brain that are associated with memory, thoughts and other cognitive functions.

Symptoms of AD typically progress in three stages:2

  • Pre-clinical stage with no symptom
  • Middle stage of mild cognitive impairment (MCI)
  • Final stage of AD dementia

The exact causes of AD is not well understood. Both genetic and environment factors are thought to play important roles in the disease process of AD.

The most important genetic factor is the presence of the apoliprotein e4 (ApoE4) allele that promote the formation of amyloid plaque.3

On the other hand, environmental and modifiable factors are thought to account for up to half of the AD cases worldwide. These factors include:3

  • Diabetes
  • Mid-life high blood pressure
  • Mid-life obesity
  • Smoking
  • Depression
  • Cognitive inactivity
  • Physical inactivity

Other plausible risk factors include:

  • Exposure to biotoxins including mycotoxins from mold, and other biotoxins from Lyme and other tick-borne pathogens. Exposure to these biotoxins, especially for genetically susceptible individuals results in chronic inflammatory response syndrome (CIRS).36
  • Exposure to neurotoxic heavy metals including aluminum, lead, cadmium and mercury.37

The underlying disease process associated with the formation of amyloid plaques and NFTs, as well as the inflammatory response and oxidative damage of brain tissues and cells, include:4–10,38

  • Obstruction to and depressed blood flow to the brain, which may be due to stroke, high blood pressure, high cholesterol levels, atherosclerosis (narrowing of blood vessels caused by plaque build-up) and arterial stiffness.
  • Insulin resistance and elevated insulin levels associated with prediabetes and diabetes.
  • Depressed glucose uptake and metabolism in certain region of the brain. The term “type 3 diabetes” has been proposed to describe AD.
  • High oxidative stress and significantly depressed non-enzymatic antioxidants (including vitamins A, C and E, lutein, zeaxanthin, β-cryptoxanthin and α-carotene), and depressed antioxidant enzyme activity (including superoxide dismutase, glutathione peroxidase and glutathione reductase).
  • Elevated advanced glycation end products (AGEs), which are highly oxidant compounds primarily resulted from dietary intake.
  • Elevated homocysteine levels.
  • Vitamin D deficiency.

There are emerging studies that showed the association between gut health and cognitive function, in particular the influence of gut microbiota (or gut flora) on the underlying inflammatory process of AD, through the gut-brain axis.34,35 (See more details how the health of our gut can influence other functions and health of our body in Why Your Gut Feeling Matter)

Because overt symptoms usually do not appear until a complex series of brain changes have occurred over decades, it is important to adopt preventive measures early on in life.

Beneficial Diets and Nutrition for AD

Dietary Patterns Studied in Clinical Research

The main types of dietary patterns evaluated in clinical research on AD include:11–19

  • The traditional Mediterranean diet*
  • The Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet**
  • Proportion of meat and dairy versus fruits, vegetables, grains and fish
  • Dietary intake of AGEs***

* The traditional Mediterranean diet emphasizes on high proportion of fruits, vegetables, legumes, grains and fish, and high intake ratio of monounsaturated fatty acids (MUFAs) to saturated fatty acids (SFAs), reduced consumption of meat and dairy products and mild-to-moderate alcohol intake.

** The MIND diet is a modified diet based on the traditional Mediterranean diet and the DASH (Dietary Approaches to Stop Hypertension) diet. It adopts a similar approach as the Mediterranean diet and the DASH in terms of emphasis on natural plant-based foods and limited intakes of animal and high saturated fat foods. In addition, the MIND diet further emphasizes on foods that were shown to be associated with neuroprotection and dementia prevention, including berries and green leafy vegetables.

*** Foods that contain the highest amount of AGEs include cooked or uncooked meat especially beef, poultry and pork, fish, and aged cheese. High and dry heat cooking also contributed to higher AGEs.

Highlights of Clinical Research Findings5,9,20–33

Based on clinical studies, a strong association between dietary patterns and the risk and progression of cognitive decline and AD has been observed among elderly population.

Dietary patterns that have been shown to reduce the risk and progression of cognitive decline and AD include the traditional Mediterranean diet, the DASH diet, and the MIND diet.

Because of the risk and contributing factors associated with AD, dietary patterns that are beneficial for reducing the risk of type 2 diabetes, high blood pressure and heart disease are also beneficial for the prevention and management of AD. See details in:

The beneficial dietary composition can be summarized as:

  • High in natural, whole plant-based foods especially fruits and vegetables and moderate amount of grains and legumes.
  • High in the ratio of unsaturated fatty acids including MUFAs (e.g. olive and avocado) and omega-3 polyunsaturated fatty acids (PUFAs) (e.g. cold water fish, flaxseed, chia seed, some nuts) over SFAs.
  • Low in SFAs and AGEs such as meat and dairy products.
  • High in neuroprotective phytonutrients including intake of berries which are rich in anthocyanidins and flavonoids, and green leafy vegetables which are rich in folate, phylloquinone, lutein and beta carotene.

Clinical trials using targeted supplementation of certain nutritional compounds have shown some positive results although the number of trials is still limited. Such nutritional compounds may include:

  • Antioxidants (vitamin E, vitamin C, β-carotene, selenium) and certain nutritional compounds (S-adenosyl-methionine, N-acetyl cysteine) to mitigate oxidative stress and imbalance.
  • B vitamins (folic acid, vitamin B6 and vitamin B12) to mitigate elevated homocysteine levels.
  • Omega-3 PUFAs for anti-inflammatory properties.
  • Acetyl-L-carnitine and MCT oil (medium chain triglycerides)**** to improve fat metabolism in the brain for fuel, thus mitigating the effect of depressed glucose metabolism associated with AD.

**** MCT are healthy form of saturated fats which is metabolized differently compared to long-chain saturated fatty acids. Food sources rich in MCT include coconut oil and palm kernel oil.

The effectiveness of the above-described diets and nutrition for AD is more prominent during early stages of cognitive decline. It is important to take preventive measure early on in life to avoid the progressive brain changes and damage.

The above-described diets and nutrition can also be beneficial for non-AD-specific cognitive decline or dementia.

 

Related Articles

Diets and Chronic Disease (Part 1: Type 2 Diabetes)

Diets and Chronic Disease (Part 2: High Blood Pressure)

Diets and Chronic Disease (Part 3: Heart Disease)

 

References

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