Metals and the risk of dementia

Copper has been the most extensively studied of the natural metals in the brain. It is not clear what role copper has in the disease.

Several studies have shown that people with Alzheimer’s disease tended to have lower levels of copper in their brains. This is in contrast to research that shows that copper is present in protein clumps in Alzheimer’s disease.

While there is some evidence that iron might be involved in Alzheimer’s disease, there is no evidence to prove that it causes the disease. It may be that Alzheimer’s disease itself causes an increase in iron levels in the brain.

Iron has also been reported in the brains of some people with Alzheimer's disease. Although, some studies have found no difference in brain iron levels in people with Alzheimer’s disease compared to healthy people. Anaemia - a condition typified by a reduction of iron in the blood - has been suggested to be a risk factor for dementia.

It is known that iron appears in the protein clumps that are associated with Alzheimer’s disease. Iron has also been shown to be abundant in the immune cells in the brains of Alzheimer’s disease patients. 

Studies have shown there is more zinc in the brains of people with Alzheimer’s disease, but less in their blood. This might be because some zinc gets trapped in the protein clumps, so doesn’t get into the blood. Studies disagree if zinc reduces the toxic effect of the protein clumps or increases it.

Reactive oxygen species (ROS) are oxygen molecules that have been altered by a chemical reaction. Increased levels are known to be damaging to cells - leading to the cells’ death - and have been seen in the brains of people with Alzheimer's disease. Copper and iron have also been implicated in the production of ROS in the brain.

Zinc, on the other hand, has been shown to protect against ROS. It does this by binding to amyloid protein in the place of copper, which reduces the creation of these ROS.

The management of these levels, and other naturally occurring metals, is very tightly controlled by the body. It includes many different molecules and disruption of these processes can occur for various reasons. It is not yet clear if there is a relationship between these metals and Alzheimer’s disease, and more research is needed.

In 1965, researchers found that rabbits injected with aluminium developed toxic protein tangles in their brains. This led to speculation that aluminium from cans, cookware and even the water supply could be causing dementia. Importantly, these results were only seen with extremely high doses - far more than we normally get from our environment.

Aluminium in food and drink is in a form that is not easily absorbed into the body. Hence the amount taken up is less than 1% of the amount present in food and drink. Most of the aluminium taken into the body is cleaned out by the kidneys. Very small amounts of aluminium are seen in the normal, healthy brain. This is considered normal and doesn’t appear to be toxic.

Case studies have described individual people who have accidentally been exposed to extremely high levels of aluminium and gone on to develop memory and thinking problems. However as these people died many years after exposure, it is impossible to say whether the aluminium exposure was connected to the damage to their brains.

The studies that look at aluminium in the brains of people with Alzheimer’s disease have mixed results. Some researchers have found aluminium in the brain but failed to show whether it was at higher levels than in healthy individuals.

Other studies have suggested that high aluminium exposure might be related to an increased risk of dementia. These studies are small and others contradict them. The levels that are considered high are far greater than people are normally exposed to.

No convincing relationship between aluminium and the development of Alzheimer's disease has been established.