[jwrallie]

Could be that reading makes you less likely to expose to dangers that could kill you by entertaining you in a safer environment, could be that reading makes you have better decisions for your health, could be that your brain has more neural connections that can be used redundantly to mask Alzheimer’s.

And what you mentioned is also combined with the above, and uncountable other relationships, causality going both ways.

[paulryanrogers]

Indeed. Which is why there must be overwhelming survey evidence before we can conclude which direction the arrow is going. Because it's unethical to isolate people and all compounding factors for a proper experiment.