What Are the Most Common Neurotoxins in Food?

Neurotoxins are chemicals that interfere with the normal function of the nervous system by damaging brain cells and tissues. The following chemicals found in food are or/may be associated with neurotoxicity:

• Mercury
• Aluminum
• Lead
• Ethanol
• Aspartame
• Monosodium Glutamate (MSG)
• Diacetyl

1. Mercury

1.1. What Is Mercury?

Mercury (Hg) is a chemical element classified as a transition metal because it becomes liquid at room temperature [1].

It is used in several applications such as thermometers, fluorescent lamps, barometers, light switches, blood pressure monitors, and float valves. Mercury exists in deferent forms:

• Inorganic mercury, including metallic mercury, mercury vapor (Hg⁰) and mercurous (Hg₂ ⁺⁺) or mercuric (Hg⁺⁺) salts
• Organic mercury, such as compounds with mercury combined with carbon atoms (methyl, ethyl, phenyl, or similar groups). 

1.2. Why Is Mercury Toxic?

Mercury toxicity is due to alteration in the structure of proteins that are essential for the function of the body’s cells, including the cells of the brain.

Mercury mainly affects the brain through its gaseous form (mercury vapor) as it is easily absorbed through the lung and the mucus membranes and reaches the brain through blood circulation.

The other forms of mercury are easily absorbed by the gut and accumulate in tissues and organs of the body.

Severe and chronic Exposure to mercury can manifest with the following symptoms:

• Mercurial tremors (involuntary and rhythmic shaking movements)
• Depression
• Anxiety
• Amnesia
• Insomnia
• Extensive irritability
• Numbness
• Muscle weakness
• Delusions
• Hallucinations

1.3. What Foods May Contain Mercury?

Exposure to mercury is due to the consumption of mercury-contaminated seafood.

2. Aluminum

2.1. What Is Aluminum?

Aluminum (Al) is a chemical element that is widely distributed in the environment. It is used in many applications such as household items (e.g., cooking utensils), building and construction, transportation (e.g., cars, trucks), and packing (e.g., cans and foil) [2].

2.2. Why Is Aluminum Toxic?

Aluminum toxicity is mainly due to its action in promoting oxidative stress resulting in free radicals which damage the DNA of nerve cells causing their death.

Other effects involve alterations in the structure of proteins are lipids necessary for the structure and function of the cells.

Aluminum reaches and accumulates in the brain through the blood circulation, extracellular fluid (fluid surrounding the cells), and cerebrospinal fluid.

The accumulation of aluminum has been associated with neurodegenerative diseases such as Alzheimer’s disease, dialysis-associated encephalopathy, Parkinson’s disease, multiple sclerosis, amyotrophic lateral sclerosis, and autism [2].

2.3. What Foods May Contain Aluminum?

Exposure to aluminum happens through drinking water, and food contaminated by aluminum in cans, cookware, and foil. Some medications, such as antacids, contain aluminum.

3. Lead

3.1. What Is Lead?

Lead (Pb) is a chemical element that is still used in many applications and industries such as batteries, shipbuilding, light industry, and machinery manufacturing.

3.2. Why Is Lead Toxic?

Lead is the most toxic heavy element causing poisoning known as saturnism. Lead accumulation in tissues generates free radicals that cause damage to the DNA of nerve cells and other cells of the body causing their death [3].

Lead accumulation in cells also interferes with DNA transcription (gene expression) and the function of enzymes involved in vitamin D synthesis and cell membrane structure.

In children, lead poisoning is associated with developmental disabilities resulting in learning difficulties, hearing loss, fatigue, irritability, vomiting, abdominal pain, loss of appetite, and weight loss.

In adults, lead poisoning manifests with symptoms such as memory loss, pain, numbness of the extremities, headache, joint and muscle pain, abdominal pain, constipation, and fatigue.

3.3. What Foods May Contain Lead?

Exposure to lead can be associated with the consumption of contaminated crops or drinking water.

4. Ethanol

4.1. What Is Ethanol?

Ethanol or alcohol is an organic chemical compound that is naturally produced by sugar fermentation or chemically through ethylene hydration.

Ethanol is used in many applications such as the production of alcoholic beverages, medical usage as an antiseptic, and as fuel and solvent.

4.2. Why Is Ethanol Toxic?

Ethanol (alcohol) induces brain damage by increasing the excitability of neurons by the neurotransmitter glutamate (excitotoxicity) [4].

Although at first, ethanol inhibits the receptor of glutamate (NMDA receptor) which reduces the excitability of neurons by glutamate, chronic alcohol consumption results in the receptor becoming insensitive to ethanol action and very sensitive to excitation by glutamate.

Alcoholism or excessive consumption of alcohol can lead to a disorder known as Wernicke-Korsakoff syndrome characterized by encephalopathy (brain lesions), impaired vision, ataxia, and impaired memory.

Alcoholism is also associated with a loss of neuropsychological performance such as learning, memory, abstracting, information processing, problem-solving, and visuospatial and perceptual-motor functioning [4].

4.3. What Foods Contain Ethanol?

Alcoholic beverages such as beer, wine, and spirits.

5. Aspartame

5.1. What Is Aspartame?

Aspartame is an artificial sweetener used as a sugar substitute in beverages and foods.

5.2. Is Aspartame Toxic?

Although its safe use is supported by many food agencies around the world, the effect of aspartame on the body (including the brain) is controversial [5][6][7].

Some studies reported that aspartame can elevate the levels of phenylalanine and aspartic acid in the brain causing the inhibition of the synthesis and release of the neurotransmitters, dopamine, norepinephrine, and serotonin.

Other studies support its role as a stress inducer that causes the production of an excess of free radicals [8].

6. Monosodium Glutamate (MSG)

6.1. What Is Monosodium Glutamate (MSG)?

MSG is one of the most used artificial additives found in canned vegetables and soups, and processed meat.

6.2. Is Monosodium Glutamate (MSG) Toxic?

Although its safe use is supported by international bodies governing food additives [9], the effect of MSG on the body (including the brain) is controversial [10].

7. Diacetyl

7.1. What Is Diacetyl?

Diacetyl is an organic compound that naturally occurs as a product of fermentation; however, it is also synthesized by chemical manufacturers as a buttery flavoring additive for use in food such as popcorns, candies, and baked goods.

7.2. Is Diacetyl Toxic?

Although diacetyl has been associated with occupational lung disease [11], its effect on the brain is controversial [12].

Conclusion

Although evidence that supports the involvement of mercury, aluminum, lead, and ethanol in neurotoxicity is well supported by research and clinical studies, the involvement of food additives including, aspartame, MSG, and diacetyl in neurotoxicity is controversial and requires clear scientific evidence.