• Omega-3
• B Vitamins
• Amino Acids
• Essential Minerals
• Vitamin D
• Plant-Based Antioxidants
• Probiotics and Prebiotics

1. Omega3

1.1. What Are Omega3 Fatty Acids Good For?

Omega-3 fatty acids are essential for the metabolism of lipid in our body and that can only be provided by the diet.

Omega-3 fatty acids are not a single entity, but they are divided into docosahexaenoic acid (DHA), linolenic acid (ALA), and eicosapentaenoic acid (EPA) [1].

• Docosahexaenoic Acid (DHA)

Docosahexaenoic Acid (DHA) is the principal constituent of the plasma membrane of neurons found in the brain and cerebral cortex. It is also found in the retina and skin.

• Eicosapentaenoic Acid (EPA)

Eicosapentaenoic Acid (EPA) is essential for the synthesis of the vasodilator, anticoagulant, and inflammatory hormone, Prostaglandin (PG).

Eicosapentaenoic Acid (EPA) is also essential critical for the synthesis of the pro-coagulation and thrombosis factor, thromboxane, and the inflammation mediators, leukotrienes.

• Linolenic Acid (ALA)

Linolenic Acid (ALA) is involved in the regulation of blood lipids and endothelial (Vessels) function. It has also significant anti-inflammatory and anti-thrombotic effects.

1.2. Why Are Omega 3 fatty Acids Good for Mental Health?

Several studies reported that the reduction in intake of Omega 3 fatty Acids results in mood disorders [2].

Major depression and schizophrenia were also associated with reduced consumption of fish and omega 3 fatty acids [2].

The severity of depression was linked with the reduction of omega 3 fatty acids concentrations in the blood.

When comparing with healthy individuals, patients with schizophrenia had significantly lower levels of EPA and DHA.

1.3 Which Food Contains More Omega-3?

Foods that are rich in Docosahexaenoic Acid (DHA) and Eicosapentaenoic Acid (EPA) include fatty fish such as salmon, tuna, herring, mackerel, sardine, and fish oils, while flaxseed, chia, walnuts, hemp, and vegetable oils are rich in Linolenic Acid (ALA).

2. B Vitamins

2.1. What Are B Vitamins Good For?

Through their co-enzymatic (help other enzymes) activities, B vitamins are essential players in the cell metabolism of sugars, amino acids, and lipids. They are also involved in the synthesis of neurotransmitters necessary for the nervous system functions.

2.2. Why Are B Vitamins Good for Mental Health?

Alterations in the activity of neurotransmitters have been associated with changes in mood, depression, bipolar disorder, schizophrenia, and obsessive-compulsive disorder (OCD). B vitamins are essential for the synthesis of several neurotransmitters and in the conductance (transmission) of nerve impulses [3] [4].

• Vitamin B1 (Thiamine)

Through its activity as a coenzyme, vitamin B1 (Thiamine) is involved in the synthesis of the neurotransmitters, GABA, Acetylcholine, and glutamate.

• Vitamin B6 (Pyridoxine)

Through its activity as a coenzyme, vitamin B6 (pyridoxine) is involved in the synthesis of neurotransmitters, dopamine, histamine, serotonin, norepinephrine, and GABA.

• Vitamin B9 (Folate, Folic Acid)

Folate has several roles in the nervous system:

– Increases the level of the neurotransmitter, serotonin, by reducing the breakdown of tryptophan which is an essential amino acid involved in the synthesis of serotonin.

–  Through its activity as a coenzyme, folate contributes to the synthesis of the monoamine neurotransmitters, serotonin, norepinephrine, and dopamine.

– Contributes to the synthesis of compounds necessary for the energy metabolism of the brain.

• Vitamin B12 (Cobalamin)

Vitamin B12 (cobalamin) has also several roles in the nervous system:

– Through its activity as a coenzyme, vitamin B12 (cobalamin) contributes to the synthesis of the monoamine neurotransmitters, serotonin, norepinephrine, and dopamine.

– It is involved in the maintenance of myelin sheets that envelop neurons and which are involved in the transmission of nerve impulses.

– Helps the activity of folate.

2.3. Which Food Contains More B Vitamins?

• Vitamin B1 (Thiamine) is naturally present in food such as whole grains, legumes, and fish.

• Vitamin B6 (Pyridoxine) is mainly found in meat products such as Beef, pork, and fish.

• Vitamin B9 (Folate) is found in many types of food; however, due to its instability (e.g., high heat cooking), it is being added to several food sources as a fortifier to prevent a vitamin B9 deficiency.

• Vitamin B12 (Cobalamin) is naturally present in foods such as meat, liver, milk, clams, fortified breakfast cereals, and eggs.

3- Amino Acids

3.1. What Are Amino Acids Good For?

Amino acids are the building blocks of proteins that are essential for life. Proteins are a vital part of building cells, tissues, and organs. They are also critical for their functions as all physiological processes of the cells require proteins.

3.2. Why Are Amino Acids Good for Mental Health?

Amino acids play a critical role in the function of the nervous system and in mental health. The amino acid glutamate is a neurotransmitter, while other amino acids are necessary for the synthesis of several neurotransmitters.

• The neurotransmitters dopamine, norepinephrine, and epinephrine are made from the amino acid, Tyrosine, that is also made from phenylalanine.
• The neurotransmitter serotonin is made from tryptophan

3.3. Which Food Contains More Amino Acids?

Foods that are rich in amino acids include meats, eggs, and milk, and other dairy products.

4- Essential Minerals

4.1. What Are Essential Minerals Good For?

Essential minerals are essential for life through their role in the production of energy, bone formation, nucleic acid synthesis (DNA and RNA), hemoglobin synthesis, and metabolism of the cells.

4.2. Why Are Essential Minerals Good for Mental Health?

• Zinc

Zinc is involved in the regulation of gene expression and protein synthesis. As a cofactor for many enzymes, zinc is involved in several metabolic reactions.

 Zinc intake has been associated with a reduced incidence of depression [5]. Zinc deficiency is also involved in learning impairment and olfactory dysfunction [6].

• Iron

Iron is essential for the production of energy (ATP) in the brain. As a coenzyme, Iron is involved in the synthesis of the neurotransmitters, serotonin, dopamine, norepinephrine, and epinephrine [4].

• Magnesium

Magnesium is involved in several mental health disorders, including anxiety, depression, and migraine.

Magnesium has an essential role in neurotransmission and neuromuscular transduction through its protective function against excitotoxicity (excessive transmission by neurotransmitters) [7].

4.3. Which Food Contains More Essential Minerals?

• Foods that are rich in Zinc include oysters, beef, lobster, pork, cereals, crab, chicken, pumpkin seeds, baked beans, dairy products (milk, yogurt, cheese), cashews, chickpeas, and oatmeal.

• Foods that are rich in Iron include dark-green leafy vegetables, nuts and seeds, meat, fish, tofu, eggs, brown rice, and dried fruit.

• Foods that are rich in Magnesium include green leafy vegetables, such as spinach, nuts, seeds (chia and pumpkin seeds), legumes, and whole grains

5. Vitamin D

5.1. What Is Vitamin D Good For?

Vitamin D is involved in the intestinal absorption of magnesium, phosphate, and calcium necessary for calcium homeostasis and bone metabolism.

5.2. Why Is Vitamin D Good for Mental Health?

A study reported the involvement of vitamin D in schizophrenia associated with low levels of maternal vitamin D during pregnancy [8].

Another study reported an association between low levels of vitamin D and depression [9].

5.3. Which Food Contains More Vitamin D?

Vitamin D is naturally found in many foods such as beef liver, cod liver oil, eggs, salmon, tuna, mackerel, and sardines.

6. Plant-Based Antioxidants

6.1. What Are Plant-Based Antioxidants Good For?

Plant-Based Antioxidants prevent oxidative stress damage to cells that can lead to their death. They perform this action by neutralizing free radicals.

6.2. Why Are Plant-Based Antioxidants Good for Mental Health?

Unbalance in plant-based antioxidants such flavones, polyphenols, flavonoids, phytoestrogens, and catechins, has been shown to promote anxiety and depression.

Plant-based antioxidants prevent anxiety and depression through their role in reducing the inflammation of brain cells and restoring balance to neurotransmitters [10].

6.3. Which Food Contains More Plant-Based Antioxidants?

Foods that are rich in plant-based antioxidants include oilseeds, legumes, tree nuts, plants of the Lamiaceae family, tea and coffee, cereals, fruits, and berries.

7. Probiotics and Prebiotics

7.1. What Are Probiotics and Prebiotics Good For?

Probiotics are the gut’s most known “good bacteria” that are Lactobacillus and Bifidobacterium. These bacteria help other gut bacteria by providing them with nutrients that are commonly known as prebiotics [11].

The most common prebiotics are fructooligosaccharides, galactooligosaccharides, and trans-galactooligosaccharides, but other prebiotics plays important roles in health and aging such as insulin enriched-oligofructose, lactulose, and oligofructose.

7.2. Why Are Probiotics and Prebiotics Good for Mental Health?

The administration of prebiotics such as non-starch polysaccharides was shown to improve the performance of working and recognition memory and cognitive functions [16][17].

 Another prebiotic known as insulin enriched-oligofructose enhances mood and immediate memory [18].

Lactulose was also shown to improve cognitive function and health-related quality of life [19].

7.3. Which Food Contains More Probiotics and Prebiotics?

Probiotics are found in yogurt, lactobacillus milk, some cheeses such as Gouda, cheddar, cottage cheese, and mozzarella, pickles, sauerkraut, kefir, kimchi, tempeh, kombucha, and miso.

Prebiotics are found in carrots, quinoa, radishes, onions, chicory roots, konjac roots, oats, yams, garlic, barley, wheat bran, berries, apples, asparagus, bananas, leeks, chia seeds, flax seeds, cocoa, coconut, jicama root, and dandelion greens.

Conclusion

Although sometimes we are not aware of the importance of the food we consume, consuming the right nutrients such as omega 3 fatty acids, B vitamins, plant-based antioxidants, probiotics and prebiotics, essential minerals, vitamin D, and amino acids can make a big difference in preventing or reducing mental health issues.

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• Scurvy
• Anemia
• Dermatitis
• Megaloblastic anemia
• Beriberi
• Rickets
• Osteomalacia
• Hemolytic anemia
• Birth defects

I. Types of Vitamins and Their Function in the Body

There are two types of vitamins: water-soluble and fat-soluble vitamins.

1- Water Soluble Vitamins

Most water-soluble vitamins are used immediately by the body and any surplus is eliminated through urine; however, vitamin B12 can be stored in the liver for a prolonged period.

Vitamin B1 (Thiamine)

Vitamin B1 is required for the production of ATP (energy) and for the metabolism of glucose, proteins, and fats by our body cells. It is naturally present in food such as whole grains, legumes, and fish [1].

Vitamin B2 (Riboflavin, Vitamin B₂)

Vitamin B2 is an essential partner for different enzymes that are required for cellular respiration and energy production, including oxidoreductases and flavine adenine dinucleotide (FAD) [2].

Vitamin B2 is naturally present in food including almonds, eggs, meat, milk and dairy products, mushrooms, and green vegetables.

Vitamin B3 (Niacin, Niacinamide)

Vitamin B3 is essential for the synthesis of nicotinamide adenine dinucleotide (NAD), a coenzyme (work together with an enzyme) necessary for the metabolism of cells (e.g., redox reactions), DNA repair, and calcium mobilization within the cells of the body [3].

It is naturally available in food such as eggs, meat, milk, and beans.

Vitamin B5 (Pantothenic Acid)

Vitamin B1 is found in most food and is required for the synthesis of coenzyme A involved in the synthesis and oxidation of fatty acids that are necessary for the production of hormones, energy production from fats, fat storage, and the transfer of information within the cell (signaling) [4].

Vitamin B6 (Pyridoxine, Pyridoxamine)

Vitamin B6 is an essential coenzyme involved in the metabolism of glucose, fat, and proteins [5]. It is mainly found in meat products such as Beef, pork, and fish.

Vitamin B7 (Biotin)

Vitamin B7 is a coenzyme for enzymes that are involved in fatty acids synthesis, gluconeogenesis (glucose metabolism), chromatin stability, and gene expression [6].

It is naturally available in food such as beef liver, salmon, nuts, eggs, avocadoes, pork, and sweet potatoes.

Vitamin B9 (Folic Acid, Folate, Folacin)

Vitamin B9 is required for DNA synthesis and for the activation of vitamin B12 [7]. Many types of food contain vitamin B9; however, due to its instability (e.g., high heat cooking), it is being added to several food sources as a fortifier to prevent a vitamin B9 deficiency.

Vitamin B12 (Cyanocobalamin)

Vitamin B12 is a coenzyme involved in fatty acids and protein metabolisms, DNA synthesis, red blood cells’ maturation, and myelin synthesis (a protein covering neurons) [8].

 It is naturally present in foods such as meat, liver, milk, clams, fortified breakfast cereals, and eggs.

Vitamin C (Ascorbic Acid)

Vitamin C is a well-known antioxidant that also functions as a coenzyme in many enzymatic reactions associated with collagen synthesis, wound healing, and the immune system [9].

 It is naturally available in citrus fruits, guava, kiwifruit, strawberries, brussels sprouts, broccoli, and bell peppers.

2- Fat-Soluble Vitamins

This family of vitamins requires fat and bile acids to be absorbed by the intestine through a process named micellar solubilization.

The Vitamin A Group

Vitamin A is not a single entity but is rather a group of compounds that include retinol, retinal, and carotenoids such as beta-carotene.

These compounds are involved in growth and development, vision, immune response, and genetic regulation [10].

They are naturally found in many foods such as fish and beef liver, cod liver oil, green vegetables (e.g., kale, spinach), carrots, and dairy products (cheese and butter).

The Vitamin D (Calciferol) group

Vitamin D is also a group of compounds that include ergocalciferol (vitamin D₂) and cholecalciferol (vitamin D₃).

They are involved in the intestinal absorption of magnesium, phosphate, and calcium necessary for calcium homeostasis and bone metabolism [11].

They are naturally found in many foods such as beef liver, cod liver oil, eggs, salmon, tuna, mackerel, and sardines.

The Vitamin E group

Vitamin E is another example of a group of vitamin compounds that include the antioxidants tocopherols and tocotrienols that protect the body’s cells from reactive oxygen species [12]. They are naturally available from wheat, seeds, and nuts oils.

Vitamin K (Phylloquinone, Menaquinones)

Vitamin K includes two compounds known as vitamin K₁ (Phylloquinone) and vitamin K₂ (Menaquinones) that are involved in blood coagulation and in the regulation of calcium attachment to the bones [13].

Phylloquinone is naturally found in leafy green vegetables, while menaquinones naturally exist in food such as chicken and beef meat, mollusks, and dairy products (e.g., cheese, yogurt, and milk).

II. Vitamin Deficiency

There are several conditions, diseases, and disorders due to vitamin deficiencies, and here is an overview of the most known ones.

1- Vitamin B1 Deficiency

• Beriberi is a rare genetic disease characterized by effects on the nervous and cardiovascular systems. It may manifest with increased heart rate, swellings of the legs, speech difficulty, mental confusion, and shortness of breath [14].
• Wernicke Encephalopathy is caused by neurological damages that manifest with symptoms of confusion, ataxia (absence of voluntary movements coordination), and ophthalmoparesis (uncontrolled movement of the eye muscles)  [15].

2- Vitamin B2 Deficiency

• Ariboflavinosis is characterized by lesions on the lips and around the corners of the mouth, the nose, and the eyes. In extreme cases, neurological, reproductive, hepatic, and anemic disorders are observed [16].

3- Vitamin B3 Deficiency

• Pellagra is associated with soreness of the mouth, diarrhea, inflamed skin, and dementia [17].

4- Vitamin B5 Deficiency

• Paraesthesia manifests with abnormal and painless sensations in the skin of arms and legs [18].

5- Vitamin B6 Deficiency

• Anemia, that is due to vitamin B6 deficiency, is associated with reduced synthesis of the heme, a necessary component of hemoglobin [19].

6- Vitamin B7 Deficiency

• Dermatitis is associated with dryness and inflammation of the skin leading to rashes and lesions on the face [20].
• Enteritis manifests with symptoms such as fatigue and tiredness, nausea, and vomiting.

7- Vitamin B9 Deficiency

• Birth Defects are associated with abnormal development of the embryo neural tube (brain and spinal cord development) during pregnancy [21].

8- Vitamin B12 Deficiency

• Megaloblastic Anemia is due to the reduction in DNA synthesis associated with the production (proliferation) of red blood cells [22].

9- Vitamin C Deficiency

• Scurvy manifests with symptoms of tiredness and fatigue, sore arms and legs, gum disease, and bleeding from the skin [23].

10 – Vitamin A Deficiency

• Night Blindness is associated with the difficulty of adaptation of the vision from day to night usually due to an anomaly with the retina [24].
• Keratomalacia affects the cornea and conjunctiva of the eye that looks cloudy and opaque resulting in blindness [25].

11- Vitamin D Deficiency

• Rickets (Osteomalacia) is characterized by soft bones in children that lead to bone deformities [26].  

12- Vitamin E Deficiency

Hemolytic Anemia is associated with rupture or breakdown of red blood cells due to the lack of antioxidant protection from vitamin E (antioxidant effect) [27].

13- Vitamin K Deficiency

• Bleeding is due to a defect in the coagulation as vitamin K is required for clot formation to stop bleeding.
• Diathesis is characterized by increased bruising and bleeding.

III. Vitamin Overdose

Vitamin overdose or hypervitaminosis is associated with excessive reserves of vitamins in the body that lead to toxicity, irritability, and overexcitement.

1- Vitamin B3 Overdose

Vitamin B3 overdose can cause flushing with headache, dizziness, and sensations of burning and itching. In certain cases, it can lead to liver damage [28].

2- Vitamin B6 Overdose

The overdose of B6 is associated with neuropathies due to nerve damage such as sensory ataxia (absence of voluntary movements coordination), abnormal and painless sensations in the skin of arms and legs (paraesthesia), and areflexia (absence of muscle reflexes) [29].

3- Vitamin B9 Overdose

An overdose of this vitamin results in nerve damage resulting in neuropathies. It also causes proprioception characterized by difficulty and uncoordinated walking and clumsiness [29].

4- Vitamin A Overdose (Hypervitaminosis A)

Vitamin A overdose has a wide effect on mental health such as depression, dizziness, and mental dullness, and on the liver (toxicity), skin (dry skin), cheilosis (inflammation of the mouth corners), gingivitis, muscle, and joint pains, and fatigue [30].

5- Vitamin D (Hypervitaminosis D) overdose

An overdose of vitamin D manifests with large disorders such as hypercalcemia, hypertension, ectopic calcifications, renal stones, hyperphosphatemia, polyuria and polydipsia, anorexia, depression, nausea, vomiting, and constipation [31].

6- Vitamin E overdose

An overdose of this vitamin results in muscle weakness, fatigue, nausea, and diarrhea. However, higher intake can lead to hemorrhagic stroke and premature death [32].

7- Vitamin K Overdose

An overdose of this vitamin, when consumed orally, is not toxic; however, it can cause toxicity in infants administered with a synthetic precursor (Menadione). Toxicity includes hemolytic anemia, jaundice due to hyperbilirubinemia (increase bilirubin in the blood), and brain damage [33].

Conclusion

Vitamins are essential for the function of the body as they are involved in key metabolic pathways. Although deficiencies in vitamins are low in developed countries, other places in the world are still affected due to malnutrition.

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This accumulation results in loss of neurons in the hippocampus and cerebral cortex, leading to progressive cognitive decline such as memory defects.

A connection between the brain and the gastrointestinal tract has been suggested due to the significant influence of the gastrointestinal flora (microbiome or microbiota) over the brain-gut axis [1] [2].

1. What Is the Role of Gut Flora in Alzheimer’s Disease?

The gastrointestinal tract is full of harmless bacteria that positively affect our health and contribute to our body’s natural processes. However, unbalance of the gut flora (Dysbiosis) can lead to significant pathological changes that can affect our immune system and brain functions.

This unbalance is due to several reasons such as a dietary change, accidental chemical consumption (unwashed pesticides on fruit and vegetables), alcohol consumption, inflammation, and excessive antibiotics’ medication.

2- What Is the Role of Dietary Changes in Alzheimer’s disease (AD)?

To reduce the risk of losing neurons in the hippocampus and cerebral cortex, responsible for the progressive cognitive decline (memory loss), it is necessary to consume food that is rich in compounds that promote and maintain the survival of neurons and their connectivity to each other.

• Glutathione

Glutathione is an antioxidant that prevents damage to neurons that are caused by reactive oxidative stress, such as free radicals, and heavy metals.

Substances that are metabolized in the liver and excreted in the bile require conjugation with glutathione to facilitate their absorption by the gut circulation [3].

Glutathione is mainly found in foods such as beef, poultry, eggs, milk, avocados, strawberries, oranges, blueberries, watermelon, peaches, and grapefruit.

• Polyphenols

Polyphenols are organic compounds that include flavonoids, such as quercetin, and epigallocatechin gallate. Quercetin is an inhibitor of the enzyme, BACE-1 (beta-amyloid precursor protein–cleaving enzyme 1) that has a role in the formation of beta-amyloid plaques [4].

In the gut, the microbiota transforms polyphenols into neuroprotective polyphenols that protect neurons during Alzheimer’s disease [4].  

Foods that are rich in polyphenols include cocoa products, blueberries, various spices, dried herbs, flaxseed, nuts (chestnut, hazelnut), olive and artichoke heads. 

• Curcumin (Turmeric)

Curcumin is a bioactive polyphenolic extract of turmeric that is used as a spice, food additive, and herbal medicine.

Curcumin has antioxidant, anti-inflammatory, metal binding, and neuroprotective activities that improve the cognitive functions in patients with Alzheimer’s disease (AD) [5]. 

In the gut, curcumin was suggested to favor beneficial bacteria by increasing the abundance of Bifidobacterium and Lactobacilli and reducing pathogenic bacteria such as Prevotellaceae, Enterobacteria, Enterococci, and Coriobacteriia that can affect brain health [6].

• Vitamin B6

Vitamin B6 is an essential coenzyme involved in the metabolism of glucose, fat, and proteins [7]. Vitamin B6 is also involved in lowering the level of homocysteine (made from methionine) in the blood by converting it into cysteine.

An increased homocysteine level (hyperhomocysteinemia) can result in blood vessels damage, including vessels in the brain which can affect nutrients supply to neurons leading to their death by starvation [8].

In the gut, Vitamin B6 (microbial vitamin B6) can be produced by bacteria such as Bacteroidetes and Proteobacteria, where it also contributes to the gut immunity to ensure the proper function of the gut in nutrients absorption [9].

Vitamin B6 is mainly found in meat products such as Beef, pork, chicken, and fish.

• Vitamin B12

Vitamin B12 is a coenzyme involved in fatty acids and protein metabolisms, DNA synthesis, and maturation of red blood cells.

It is also necessary for the production of myelin, a protein covering neurons, and necessary for the nervous system function through its role in the transfer of nerve impulses and metabolic support of neurons [10].

Like vitamin B6, vitamin B12 also reduces homocysteine level (hyperhomocysteinemia) and prevents the damage of blood vessels, including vessels of the brain which, and therefore, can affect nutrients supply to neurons leading to their death by starvation [11].

In the gut, certain bacteria and archaea produce vitamin B12 during food fermentation.

It is naturally present in foods such as meat, liver, milk, clams, fortified breakfast cereals, and eggs.

• Folic Acid (Vitamin B9)

Vitamin B9 is required for DNA synthesis and for the activation of vitamin B12, and therefore, indirectly plays an important role in protecting blood vessels from damage, including the brain blood vessels [12].

Many bacteria in the gut produce an active form of folic acid known as tetrahydrofolate (THF), including Bacteroides, firmicutes, actinobacteria, fusobacteria, and proteobacteria.

Many types of food contain vitamin B9; however, due to its instability (e.g., high heat cooking), it is being added to several food sources as a fortifier to prevent a vitamin B9 deficiency.

• Unsaturated Fatty Acids

Unsaturated Fatty Acids are parts of phospholipids that are necessary for the formation of the membranes of cells, including neurons. One of the most known unsaturated Fatty Acids is omega-3 polyunsaturated fatty acids [13].

In the gut, the microbiota regulates the availability and absorption of unsaturated fatty acids

Foods that are rich in omega-3 polyunsaturated fatty acids include salmon, sardines, and mackerel.

• Lecithin

Lecithin is a fatty substance composed of a mixture of phospholipids that are rich in choline, a necessary component of the neurotransmitter acetylcholine that is involved in memory, mood, muscle, and nervous system functions [14].

In the gut, food that contains lecithin is digested by the pancreas and mucosal enzymes to produce choline that is absorbed by the gut circulation.

Lecithin is mainly found in foods such as meat, poultry, fish, dairy products, and eggs.

• Caffeine

Caffeine is a stimulant of the central nervous system where it has effects on learning, memory, alertness, and concentration. Caffeine has antioxidant effects and may protect against cell damage, including damages to neurons, by reducing oxidative stress [15].

Beverages, such as coffee, tea, soft and energy drinks, are digested by the gut flora to generate caffeine that is absorbed by the intestine’s circulation.

• Prebiotics

The most common prebiotics are fructooligosaccharides, galactooligosaccharides, and trans-galactooligosaccharides, but other prebiotics plays important roles in health and aging such as insulin enriched-oligofructose, lactulose, and oligofructose [16].

They are indigestible carbohydrates that are fermented and broken down by probiotics to obtain survival energy, and short-chain fatty acids such as lactic acid, butyric acid, and propionic acid.

The administration of prebiotics such as non-starch polysaccharides was shown to improve the performance of working and recognition memory and cognitive functions [17].

Prebiotics are found in carrots, quinoa, radishes, onions, chicory roots, konjac roots, oats, yams, garlic, barley, wheat bran, berries, apples, asparagus, bananas, leeks, chia seeds, flax seeds, cocoa, coconut, jicama root, and dandelion greens.

• Probiotics

The gut contains beneficial bacteria known as good bacteria, such as Lactobacillus and Bifidobacterium. These bacteria help other gut bacteria produce nutrients for the body by providing them with nutrients that are commonly known as prebiotics [18].

Probiotics are found in yogurt, lactobacillus milk, some cheeses such as Gouda, cheddar, cottage cheese, and mozzarella, pickles, sauerkraut, kefir, kimchi, tempeh, kombucha, and miso.

3- What Is the Role of Alcohol in Alzheimer’s disease (AD)?

Excessive consumption of alcohol for a long period can damage the brain and reduce the size of the brain white matter responsible for signal transmission in the brain.

It can also cause a deficiency in vitamin B1 resulting in diseases such as Korsakoff’s syndrome characterized by alterations in short-term memory [19].

4- What Is the Role of Pesticides in Alzheimer’s disease (AD)?

Pesticides are neurotoxins that can induce oxidative stress, the fibrilization of tau and alpha-synuclein (formation of amyloid fibrils), alteration in the function of mitochondria, and the loss of neurons [20].

People such as gardeners and farmers that use pesticides for their activities are at higher risks of neurodegenerative diseases such as Alzheimer’s disease (AD).

Accidental consumption of pesticides associated with unwashed pesticides on fruit and vegetables can also increase the risk of developing Alzheimer’s disease (AD).

5- What Is the Role of Excessive Antibiotic Medication in Alzheimer’s disease (AD)?

Excessive use of antibiotics can cause an imbalance in the gut flora (microbiota) and affect the function of the probiotic population necessary for the generation of essential nutrients to the function of the body organs, including the brain [21].

6- What Is the Role of Neuroinflammation in Alzheimer’s disease (AD)?

Imbalance of the gut flora (Dysbiosis) can lead to disruptions in the gastrointestinal permeability and blood-brain barrier, that are due to the secretion of amyloid and lipopolysaccharides (LPS), known to modulate the inflammatory signaling pathway leading to neuroinflammation, neuronal injury, and ultimately to neuronal death in Alzheimer’s disease (AD) [1] [22]. 

Conclusion

To reduce the risk of Alzheimer’s disease (AD) that could be associated with an unbalance in the Gut flora (Dysbiosis), a healthy diet and the implementation of a healthy nutritive plan throughout a life of an individual is necessary.

Intake of pre-and probiotics, vitamins (B-complex vitamins), calcium, magnesium, zinc, and beta-carotene, can help prevent dysbiosis, while the consumption of processed meat, high carbohydrates containing food, and dairy products as well as excessive use of antibiotics, may promote dysbiosis.

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