science

Hmmm...

I remember doing some (non-professional) research on marital status and life outcomes, and I recall there being a correlation between marital status and life expectancy -- marriage led to longer lifespans.

I could be mistaken.

But if I'm not, could it be that the unmarried die earlier, and thus are less likely to have acquired dementia of any type?

The associations for divorced and never married remained significant accounting for demographic, behavioral, clinical, genetic, referral source, participation, and diagnostic factors. The associations were slightly stronger among professional referrals, males, and relatively younger participants.

(Not sure what "demographic" covers...)

Males also tend to live shorter lifespans, especially when unmarried, IIRC...

The temptation to send it to my spouse is high

The people who had always been single (never married) had the lowest risk of all, though the difference between them and the other unmarried groups was not statistically significant.

Selection bias...

A frightening amount of people get married because they're worried about having someone to take care of them at an elderly age. Even if their goal is recipical, for a lot of people that's a big driver for marriage.

People who are more self sufficient and with a strong family health history doesn't have that drive.

Couple that with not being able to "offload" tasks to a spouse and you end up with single people staying active mentally which is one of the biggest negative correlations to Alzheimer's.

another day another win

So the hypothesized mechanism here is that single people tend to have healthier social lives. Another study that accounts for level of social activity might be needed to untangle this. But this does support the idea that the issue is not marriage per se but the atomized nuclear family we’ve built up as the highest form of human relationship in the West. It seems very possible to build a society that has plenty of marriage but also healthy extra-marital relationships.

I would be curious if there’s also a correlation with car and suburban culture which are strong elements that separate families from outside socialization in our culture, especially for the elderly who may eventually lose the ability to drive.

Direct link to the study:
https://alz-journals.onlinelibrary.wiley.com/doi/10.1002/alz.70072