The risk factors for Alzheimer's disease: a review and a hypothesis.

More than 20 risk factors for Alzheimer's disease (AD) have been proposed in the literature. The evidence for them is examined in this review. Amongst those that appear likely to be true risk factors, an attempt is made to identify a common mechanism to which they might contribute. There is some support for a hypothesis that the formation of amyloid plaques is due to the activity of free oxygen radicals. This would be consistent with the association between AD and late age, a family history of Down's syndrome, vascular dementia, head injury, and exposure to phenacetin, organic solvents or vibrating tools. This hypothesis provides a theory-driven lead in the search for further risk factors; if upheld, it would suggest a strategy for treatment and for prevention.