Alzheimer's disease Laura Mc Kay Loreto College Colerain Chemistry Key Skill AS Level

How can chemicals affect the body?
Aluminium and Alzheimer’s Disease.
By Laura Mc Kay
Y13 ICT Key Skill Assignment
2002

Alzheimer's disease is a chronic illness that is characterised by gradual loss of memory and mental powers to think and to reason, with emotional instability and eventually impaired brain functions for daily living. Pathological studies have shown that it kills brain cells and leaves an accumulation of unusual protein substances associated with damage to nerve cells called Neurofibrillary Tangles (NFT) and scars called Senile Plaques (S.P.).

The possibility of a link between aluminium and Alzheimer's disease surfaced in the 1960s as a result of a study finding elevated levels of aluminium in the brains of Alzheimer's diseased patients after their death. Using electron probe microanalysis found varying levels of aluminium and silicon in about half the tangles and plaques in the brain of Alzheimer's patients. There is circumstantial evidence linking aluminium with Alzheimer's disease but it is impossible to say so far whether aluminium may be a definite cause.

This computer graphic shows a vertical (coronal) slice through two different brains. The brain on the left is that of an Alzheimer patient, while that on the right is of a normal, healthy brain. The Alzheimer brain shows considerable shrinkage and the tangled fibres.

Aluminium

Aluminium is the world's most common metallic element. It makes up about 8% of the Earth's crust. It occurs in various forms mostly as oxides in rocks and soils, in vegetation and in water.

Aluminium metal has a low density and can be easily formed into many shapes and objects. These valuable properties make it responsible for its widespread use in the transport, building, food processing, packaging and pharmaceutical industries.

Aluminium can be consumed in many ways, the following are just a few ways which I will go into more detail about:

Under acidic conditions, however, aluminium is released from rocks and soils in a soluble form which can be absorbed by plants and animals. Researchers therefore look at the combined effect on human health from natural exposure to metals present in food, water and air, as well as from those additions resulting from the use of utensils, food wrappings and medicine.

Most vegetation contains aluminium compounds. Plants absorb limited quantities from the soil. However, some take up larger quantities and for this reason are called "accumulator" plants. The tea bush is an example of an accumulator.

Studies have found that beverages (tea, coffee and soft drinks) and cereals (cakes, puddings, biscuits, breakfast cereals, bread, flour, oatmeal and rice) are our main sources of aluminium from food.

Some aluminium is naturally present in food but some, in the form of aluminium salts, is added for various purposes. Aluminium-based additives are widely used in bleaching, in preserving and pickling processes, and in powdered foods such as instant coffee, dried milk, artificial ‘creamers’ and table salt. Bread, cake, biscuits and baking powders may be high in aluminium if they contain aluminium food additives. Four aluminium additives have E-numbers: E173, E541, E554 and E556. Others are shown by name in additive listings on foods. Additive E173 is powdered aluminium. Its only permitted use is for coating a range of sweets from small cake decorations to sugared almonds.

Aluminium in the diet of an average adult usually ranges from about 5 mg per day to 12 mg per day, although people on special medication may receive more than 1000 mg per day, usually as aluminium hydroxide The main aluminium compound used in medicine is aluminium hydroxide. This is used as an antacid in the treatment of gastric ulcers and as a phosphate binder in cases of long standing renal failure. The most convenient way to reduce phosphate absorption from the gut in order to prevent this is to give aluminium hydroxide which binds the phosphate from the food to produce insoluble aluminium phosphate, which is not absorbed.

Alternative antacids do exist but they are not as efficacious or safe. Antacids make the stomach more alkaline, and this prevents the absorption of most of the aluminium. Aluminium absorption is higher if antacids are taken with orange juice instead of water.

When the ability of the kidneys to excrete aluminium is impaired, accumulation of aluminium compounds in the body may occur. Patients with kidney failure face a multitude of problems, including the inability to excrete absorbed aluminium. Toxicity associated with exposure to aluminium in the dialysis fluid, or with the long-term medical use of aluminium compounds in this patient group is recognised. Care is taken to monitor blood levels of aluminium in anyone with kidney failure. The acute "dialysis dementia" described in the early days of renal dialysis has no connection with Alzheimer's disease.

A recent survey suggests that rates of Alzheimer's disease are higher in areas with the highest level of aluminium in the water supply. The disease was approximately one and a half times more frequent in districts with higher levels of aluminium in the water, compared with those in which it was low or absent. This is a relatively small increased risk and the researchers agree that this research is inconclusive, raising more questions than answers.

Recent reports suggesting that fluoride in water increases the aluminium dissolved from cooking utensils have been disproved

Your intake of aluminium from water is very small. But some scientists think the aluminium in water is in a form that's easier for your body to absorb.

Aluminium is naturally present in some water. In addition, aluminium sulphate is widely used in the filtering of public water supplies. The European standard is not based on any estimate of possible health risk, but on aesthetic considerations of water colour. Most people's water in the UK has less aluminium that 0.2mg in a litre.

Aluminium also occurs naturally in most water supplies and as part of dust particles in the air that we breathe.

There isn't much you can do about aluminium in the air. Your intake from the air is in any case negligible. Some inhaled aluminium enters your lungs, but hardly any enters the rest of your body.

Aluminium oxide, which forms on the surface of all aluminium metal in the presence of air, is stable in the pH range of 4.5 to 8.5, making aluminium suitable for storage of many different food types. Your food may also come into contact with aluminium from packaging, foil trays, foil lined cartons and aluminium cans. Or you may cook or store food in foil.

The amount of aluminium added to most foods by freezing, storing and cooking it in foil or disposable aluminium trays is negligible.

Most foil-lined cartons or aluminium cans have a layer of lacquer, plastic or cardboard covering the metal and the food or drink picks up very little aluminium or often a protective polymer coating covers the aluminium.

The aluminium added to most foods by cooking in uncoated aluminium pans is less than 0.1mg per 100 gram serving. But the acid in some foods can increase the amount of aluminium in food picks up from uncoated aluminium pans.

Rhubarb cooked in an uncoated aluminium pan or pressure cooker can, for example, pick up 4mg of aluminium per 100g serving. Adding sugar can halve the amount of aluminium dissolved. If you want to reduce your aluminium intake from cookware, you could avoid cooking acidic goods (most fruits) in uncoated aluminium pans.

Cooking food in coated/non-stick or hard-anodised aluminium pans adds virtually no aluminium. Coated or non-stick pans are easy to distinguish from uncoated pans. Hard-anodised aluminium pans are steely grey or black colour. It is best not to clean uncoated aluminium pans with cleaning soda or bleach. These strip away the surface of pans, leaving newly exposed metal, which is more likely to dissolve into food. Acidic food stored in uncoated aluminium cookware can also accumulate aluminium.