I think you have this backwards. OP is saying sleep apnea is common, but we’ve only had CPAP machines to compensate for it, since the 80s. I don’t see them trying to implicate CPAP as the cause of an increase in dementia.
I think bhouston is arguing (correctly) you can’t have a 10% of the population drop in dementia prevalence by an intervention that only targets 3% of the population, so even if CPAPs contribute, that does not explain most of the drop.
(If everybody who uses CPAPs would get dementia, and they are 100% effective at preventing that, the drop would still be ‘only’ 3% of the population)
