Scientists do not know what causes Alzheimer's disease. But they have identified several risk factors that increase the likelihood of developing the disease, or suffering non-Alzheimer's cognitive decline. These risk factors run from the well-established to the speculative and highly controversial.

Alzheimer's is marked by abnormal clumps (called senile plaques) and irregular knots (called neurofibrillary tangles) of brain cells. For reasons not well understood, these plaques and tangles take over healthy brain tissue, devastating the areas of the brain associated with intellectual function