It is now clear that there is no single cause of dementia but whatever causes the disease in each person, the outcome is the same - progressive decline of brain function.

The following have been suggested as possible causes: environmental pollution, viruses, aluminium, heredity, repeated head injury (e.g. boxing) or even too little use of the brain. Indeed, all of them could contribute to progression of dementia but not all will occur in every case.

The two strongest risk factors for developing Alzheimer’s disease are age and having a close relative who is affected. This has led to an increase in the number of research programmes examining the genetic background of those with Alzheimer's disease. However, it is still not possible to absolutely predict who will develop Alzheimer's disease, even if a family member has already been diagnosed.