yeah strongly agree. it was thought that those plaques in the brain was the cause of alz; however, some research has indicated that's the body's defense against what is going on, not the cause. so you could take a medication that lowers GDF15, and its possible it actually increases the onset of dementia.

Exactly. I know if medication were to be developed, checking "are GDF15 levels significantly lowered" would be part of the trials.

But how often does the medication development process check the result we care about: "does this medication then go on to reduce the chance of dementia?"

Always. Secondary endpoints are heavily disfavored in FDA approval.