On 2016 Aug 07, David Keller commented:

What chemical forms of aluminum and types of exposure raised dementia risk most?

The U.S. Government Centers for Disease Control (CDC) hosts a Toxic Substances Portal which provides a 117-page full toxicological profile for aluminum, including a discussion of the effects of aluminum ingestion on dementia at the following URL (accessed on 8/15/2016):

http://www.atsdr.cdc.gov/toxprofiles/tp22-c3.pdf

I cannot summarize the discussion better than the following quote taken directly from the CDC website:

"The contrast between the results of the drinking water studies, many of which found a weak association between living in areas with high aluminum levels in drinking water and Alzheimer’s disease, and the tea and antacid studies may be due to the difference in aluminum bioavailability. The presence of tannins and other organic constitutes found in tea may significantly reduce aluminum absorption; the aluminum hydroxide found in antacids is poorly absorbed. Although the aluminum speciation was not provided in most drinking water studies, in a study by Gauthier et al. (2000), organic monomeric aluminum was the only aluminum species significantly associated with Alzheimer’s disease. The bioavailability of organic aluminum compounds such as aluminum citrate, aluminum lactate, and aluminum maltolate is much greater than for inorganic aluminum compounds (Froment et al. 1989a; Yokel and McNamara 1988). In conclusion, the available data suggest that aluminum is not likely the causative agent in the development of Alzheimer’s disease. However, aluminum may play a role in the disease development by acting as a cofactor in the chain of pathological events resulting in Alzheimer’s disease (Flaten 2001)."

On 2016 Aug 07, David Keller commented:

What chemical forms of aluminum and types of exposure raised dementia risk most?

The U.S. Government Centers for Disease Control (CDC) hosts a Toxic Substances Portal which provides a 117-page full toxicological profile for aluminum, including a discussion of the effects of aluminum ingestion on dementia at the following URL (accessed on 8/15/2016):

http://www.atsdr.cdc.gov/toxprofiles/tp22-c3.pdf

I cannot summarize the discussion better than the following quote taken directly from the CDC website:

"The contrast between the results of the drinking water studies, many of which found a weak association between living in areas with high aluminum levels in drinking water and Alzheimer’s disease, and the tea and antacid studies may be due to the difference in aluminum bioavailability. The presence of tannins and other organic constitutes found in tea may significantly reduce aluminum absorption; the aluminum hydroxide found in antacids is poorly absorbed. Although the aluminum speciation was not provided in most drinking water studies, in a study by Gauthier et al. (2000), organic monomeric aluminum was the only aluminum species significantly associated with Alzheimer’s disease. The bioavailability of organic aluminum compounds such as aluminum citrate, aluminum lactate, and aluminum maltolate is much greater than for inorganic aluminum compounds (Froment et al. 1989a; Yokel and McNamara 1988). In conclusion, the available data suggest that aluminum is not likely the causative agent in the development of Alzheimer’s disease. However, aluminum may play a role in the disease development by acting as a cofactor in the chain of pathological events resulting in Alzheimer’s disease (Flaten 2001)."