New study below.
It would be unfriendly to post the paper without suggestions as to how risk might be reduced.
ADT has a profound worsening effect on the symptoms of the metabolic syndrome [MetS]. MetS has an across the board negative effect on health & mortality. A paper last month reported:
"Increased risk of cognitive impairment in patients with components of metabolic syndrome." 
While there are no studies that would convince the scientists in this group, there are 180 PubMed hits for <polyphenols dementia>. A recent review paper offers a useful summary of what is known about curcumin, resveratrol, etc. 
"Exercise is associated with a delayed onset of dementia." 
The new Stanford study of "9272 men with prostate cancer (mean ... age, 66.9 ... years" reported that the risk of developing dementia was "7.9% among those who received ADT vs 3.5% in those who did not receive ADT", at five years.