Controversial claims about Alzheimer's risk factors
The charity Alzheimer's Research UK says the causes of dementia are still not yet fully understood.
Research is making progress in understanding the causes of dementia which will be essential into developing new treatments.
Over the years, various theories have been suggested and tested. What do we know?
Known risk factors
Research has found age is the greatest factor in the development of Alzheimer's disease. A family history of Alzheimer's may give marginally higher risk of developing the condition than in someone with no family history. Having Down's syndrome increases a person's Alzheimer's risk, as does suffering a severe head injury or whiplash.
One of the most publicised and controversial theories concerns aluminium, which became a suspected cause of Alzheimer's disease when researchers found traces of this metal in the brains of patients with Alzheimer's disease. Many studies since then have either not been able to confirm this finding or have had questionable results.
Aluminium is present in higher amounts than normal in some autopsy studies of Alzheimer's patients, but not in all. Further doubt about the importance of aluminium stems from the possibility that the aluminium found in some studies did not all come from the brain tissues being studied. Instead, some could have come from the special substances used in the laboratory to study brain tissue.
Aluminium is a common element in the Earth's crust and is found in small amounts in numerous household products and in many foods. As a result, there have been fears that aluminium in the diet or absorbed in other ways could be a factor in Alzheimer's. One study found that people who used antiperspirants and antacids containing aluminium had a higher risk of developing Alzheimer's. Others have also reported an association between aluminium exposure and Alzheimer's disease.
On the other hand, various studies have found that groups of people exposed to high levels of aluminium do not have an increased risk. Moreover, aluminium in cooking utensils does not get into food in significant concentration, and the aluminium that does occur naturally in some foods, such as potatoes, is not absorbed well by the body.
Overall, Alzheimer's Research UK says that despite occasional publicity, research has shown that aluminium is not a dementia risk factor.
Zinc has been implicated in Alzheimer's disease in two ways. Some reports suggest that too little zinc is a problem, others that too much zinc is at fault. Too little zinc was suggested by post mortems that found low levels of zinc in the brains of Alzheimer's disease patients, especially in a certain region.
On the other hand, another study suggests that too much zinc might be the problem. In this laboratory experiment, zinc caused beta amyloid from cerebrospinal fluid - the fluid that bathes the brain - to form clumps similar to the plaques of Alzheimer's disease.
In 2010, researchers from the Mental Health Research Institute at the University of Melbourne suggested that zinc can negatively affect the way the body deals with iron in the brain. They believe zinc may be a useful target in the study of Alzheimer's disease.