Two clues to help you as you read studies:
(1) association≠causation
(2) Level of Evidence is important in determining how much faith to put into a study
The
association of dementia and ADT has been noticed for a while. But if you think about
it, you'll see that the real cause is difficult to tease out. Older men are more likely to have dementia
and they are more likely to have prostate cancer requiring ADT; smoking, diabetes, CV disease, lack of exercise, depression, drugs used to treat other cancers, BMI, poor eating habits, etc. all increase as we age
and they are all risk factors for dementia.
In the latest study I've seen about
this, by NIH of the Medicare database, they noticed a small association for both Alzheimer's and dementia; however, after adjusting for risk factors, the association disappeared entirely. In fact, there was a very small diminution of Alzheimer's risk. Furthermore, there was no dose effect - men on ADT for longer duration had no more dementia risk than men on ADT for shorter duration.
ascopubs.org/doi/full/10.1200/JCO.2017.72.6109In the only randomized clinical trial (Level 1 evidence) I've seen related to this, they found that hypogonadal men treated with TRT had the same risk of dementia as those who did not receive TRT. So we can be certain that replacing testosterone does not prevent dementia.
/www.ncbi.nlm.nih.gov/pmc/articles/PMC5433758/Several studies have suggested a positive association:
/www.ncbi.nlm.nih.gov/pmc/articles/PMC5070576/www.tandfonline.com/doi/abs/10.1080/13685538.2016.1271782?journalCode=itam20Other studies have suggested no association:
ascopubs.org/doi/full/10.1200/JCO.2016.69.6203/www.ncbi.nlm.nih.gov/pmc/articles/PMC5507085/There will never be definitive evidence of causation or its lack. That would require a randomized clinical trial where one group got ADT and one group didn't. It would be unethical to withhold ADT from men with incurable PC. So each man has to decide whether the possibility of an increased risk is worth dying sooner.