daisya.....what an interesting question......and I have no idea of the answer, just a few points.
From the age of about 20-30 years of age, one tends to start to lose brain cells which eventually lead to memory loss in the elderly....usually short time memory loss. In simpler terms you can remember grandad taking you to Skegness and buying you an ice cream sixty years ago, but you cannot now remember where you put your purse this morning.
This is by far and away the commonest cause of memory loss and well down the league comes Dementia, Altzheimers and certain Depressive states.
Fluoridation:
I have seen no scientifically and properly conducted trials which show that fluoridation of drinking water plays any part in the onset of memory loss.
One can trawl the net, as many do, and produce scientific papers published to support your point or "rubbish it" and in my opinion this usually means that there is no widely acclaimed answer OR that is matters not a "toss"
I'm going to watch footie on TV now.