Comment Re:Couple of possibilities (Score 1) 70
In the recent past no one tracked most of these conditions that people get in old age. Alzheimers was first named in 1901. And a lot of people died young enough from various untreated common bacterial infections to reduce the size of the population old enough to even get Alzheimer's. Historical data is fairly limited, the data we have is at best poor to non-existent (not tracked, health so poor as to make what data that existed useless to compare), and for the most part we only even have useful data from that last 70 years ( before that general health of most of the population was generally so poor that a significant number of 18-25 year olds were not healthy enough to join the military in wwi, 11% had VD, 10% had TB, and there were other issues that disqualified).
Most of the "new" diseases we currently find are simply noticing some disease that was always there but our data was not good enough to identify it.
Ie like Zika. It was first identified in 1947, and at the time studies (in the area were it was found) identified that 6% of the population had anti-bodies for it, so no telling how long Zika had been around, and Yellow Fever and other similar tropical infections that were more lethal were bigger issues that would have made looking for Zika and other less lethal diseases not a priority.
So it is likely that Alzheimer's was always a problem but not really identified as anything other than one of the symptoms of "old age".