No correlation known to me, but likely still a bit of self-selection, at least for some large swaths, which can potentially bring in a confounding factor.
Yes but I'm not talking about quantity of older people in total, I'm talking about what percentage of them get a disease.
With cancer, which is also more likely the older you get, studies show that the chances of dying from it are about 12% higher in the poorest counties than wealthier counties in the US. That is despite people in those counties having a shorter lifespan from all other things as well.
So my question in response to the parent's throwaway class warfare riff was: Given two people who survive to the same age, let's say 80, is one more likely to get Alzheimers than the other based on income? The article here would suggest otherwise, given that taxi drivers and ambulance drivers are among the least well compensated workers and yet strangely have 1/3rd the rate of Alzheimers.
My point is, if you live to be 80, you won't be any less likely to get Alzheimers if you're rich. So there's not really a correlation between 90 year olds walking around NYC dementia-free and the fact that they're wealthy enough to live to 90.
I lived a couple years in a working class farm town in Spain where the old people were mostly not wealthy by but were really physically fit and mentally sharp. I think it was due to them having constant social interaction, every day walking around the plazas talking with their elderly friends. Some of these people were living alone in their mid-90s, and their diet mostly consisted of fried sardines, pork, olives, and cheap local wine. So living a good full life may be better protection against the ravages of dementia than living a wealthy one.