Introduction

Although aluminum is the second most common metal used in manufacturing after iron, aluminum has numerous potential harmful effects on the health if accumulated within the body. Its interaction with various bodily structures and with numerous physiological mechanisms determines its toxicity, especially regarding the nervous system. The cardiovascular system and the bones are other targets for aluminum-induced damages.

Nervous system effects

Aluminum is a known neurotoxin. Suggestions for its noxious effects on the brain emerged more than 100 years ago. In 1965, a research proved the presence of brain damage in rabbits exposed to aluminum. However at that time the progress of science was insufficient to be able explain the exact pathophysiological mechanisms of the aluminum's interaction with body structures. Now, when medicine has made huge progress, never seen before, medical researchers are aimed to justify the intimate interactions between aluminum and neurons in order to explain the reasons for its toxicity.

Aluminum is considered as an etiological factor in several neurodegenerative disorders, amongst which are Alzheimer's and Parkinson's disease. Other conditions such as autism, chronic fatigue syndrome, decreased immune system reactivity, learning and memory troubles could also possibly be linked with abnormal aluminum exposure.

Mechanisms

Aluminum interacts with different bodily structures through various mechanisms. Firstly, in the central nervous system, aluminum causes the formation of free radicals. Free radicals are highly reactive particles that tend to bind with different molecules and destroy them. They have the ability to interact with all cell structures- the cell membrane, the cytoplasm and the nucleus by causing destruction of lipids, proteins and DNA. Such harmed cells are unable to function properly, and they die. 

In addition aluminum interacts with calcium, magnesium and iron due to some physical resemblances between these ions. In that way aluminum disturbs the processes of transport through the cell membrane, limiting the cell supply of nutrients and the elimination of waste products. In that way aluminum not only troubles the cell metabolism but also worsens the communication between the neurons, which communication stands in the base of all physiological processes occurring within the brain, such as movement, speech and memory.

Moreover aluminum blocks some enzymes (e.g. choline acetyltransferase), preventing their normal function of catalyzing the chemical reactions within the body. All these pathological mechanisms undoubtedly lead to progressive neuronal damage and cell death.

Role of Aluminum in Neurodegenerative Disease

Parkinson's disease: As explained above, aluminum toxicity leads to serious troubles in the cell metabolism. As a protective mechanism the body induces cell death in every cell that is damaged and unable to fulfill its function. This explains the possible linkage between aluminum and Parkinson's disease. This condition is characterized by the progressive loss of dopamine producing neurons that causes tremor, changes in walk and muscle strength, dementia and emotional problems such as anxiety and depression. The exact causes for Parkinson's disease are yet not completely clarified and the condition is probably multifactorial. However, experiments on animal models showed decrease in the dopaminergic neurons in mice models exposed to aluminum. Postmortem brain specimens from patients with Parkinson's disease also demonstrated elevated levels of the element (Bolt HM, Hengstler JG, Aluminium and lead toxicity revisited: mechanisms explaining the particular sensitivity of the brain to oxidative damage).

Alzheimer's disease: Alzheimer's disease is a neurodegenerative disorder that occurs due to the formation of pathological plaques within the brain that damage the neural cells leading to a progressive and severe physical and psychological impairment. Such plaques have also been discovered in patients with aluminum toxicity. In addition similar enzyme dysfunction has been observed in both patients with Alzheimer's disease and those suffering from aluminum intoxication.  A study of 668 brains specimens from patients suffering from Alzheimer's disease, conducted in Ontario, showed that the risk of Alzheimer's disease is 2.5 times higher in patients who have consumed potable water rich in aluminum.

In the same time researches in different regions of the world, including Canada, England and Norway demonstrated increased prevalence of Alzheimer's disease in regions where the water contains more aluminum.

Other adverse effects of aluminum: As aluminum interacts with dopamine-producing neuronal cells and destroys them, the metal causes the condition known as Parkinson's disease. However, within the brain there are numerous types of neurons, not only dopaminergic ones. High levels of aluminum could damage every one of them and cause wide range of problems, including learning and memory problems, emotional instability, anxiety, depression, hyperreactivity, chronic fatigue and impaired motor functions and coordination.

Moreover, dementia has been observed in patients on chronic dialysis, treated with aluminum-containing binders. Changes in other systems, such as osteoporosis and anemia, typically caused by aluminum, were also observed in such patients, underlining one more time the toxic effects of the metal on the human brain and body.

Conclusion

Various clinical trials have proven the aluminum's toxicity on the central nervous system. Effects of aluminum can be even more pronounced in children- organisms whom are very sensitive to toxic agents, and in patients with impaired renal function due to their inability to excrete the excessive amounts of aluminum. Aluminum's period of elimination from the brain is extremely prolonged and could last up to seven years, which underlines the possibility of accumulation of the metal and the potential amplification of its harmful effects.