Correlation and causation

I was listening to a program on Alzheimer's disease on the radio this afternoon. Aside from feeling incredibly irritated with the featured artist who works with Alzheimer's patients going on and on about how his work proved that people with Alzheimer's disease aren't just vegetables like everyone says but still have memories (gosh, really? Have you ever met anyone with Alzheimer's disease before now? Like most diseases, it has a progression. It's not like people just wake up one day a complete blank), I was struck with a new thought on the oft-repeated research that people who keep their minds active are less likely to develop Alzheimer's disease.

The particular research cited today was that people who work longer are less likely to develop Alzheimer's. As I listened, I started thinking, now wait a minute. My father didn't get Alzheimer's because he retired at 62, he retired at 62 because he had Alzheimer's disease. Research shows that people start showing subtle signs of Alzheimer's disease years and years before it gets bad enough to get diagnosed. Is it that working longer keeps the disease at bay, or is it that people who aren't going to develop Alzheimer's are better able to keep working, and people who do have Alzheimer's in their future may retire earlier because they're starting to experience subtle mental deficits?

Really, if you think about it, Alzheimer's is a physical disease of the brain. I'm sure doing crosswords helps maintain nerve connections and mental agility, but can it really prevent plaque formation? Almost certainly not. I suspect again that the research that shows that people who do crosswords are less likely to get Alzheimer's is because people who are developing Alzheimer's have trouble doing things like crosswords.

I'm not saying that doing activities that keep your brain sharp can't help your mental acuity if you do start developing Alzheimer's or dementia. My father's doctor said that the reason he stayed relatively high functioning as long as he did is that he was so intelligent, and therefore had a lot more function to lose before it really started to show. The better your brain works, the more resilient it will be in compensating if it starts to break down.

But this seems like yet another example of how studies that show correlations somehow get turned into the gospel of how you can control your health, that if you're just virtuous enough you'll be well-nigh immortal, and consequently how much you are to blame if you somehow get sick anyway.