Are you're implying that there is a third factor that both reduces risk of dementia by 10x and increases risk of kidney failure by 10x? I think that's highly unlikely.
Or theoretically getting dementia a decade later could protect against organ failure a decade earlier.
But I really don't think that's it. If this data is right there is probably an effect. I agree with the author that the mostly likely reason this isn't true is because of bad data.
> - How are the patients selected for transplants? Scarce organs are probably not given to patients who have other serious impairments as well.
Even though being healthy helps move you up the list of organ transplant recipients. It would still be really strange if people who got organ transplants were healthier than the general population, who mostly do not need organ transplants.
>- How were the (non)-dementia patients assessed? No formal diagnosis of dementia != no dementia.
But it would be weird if organ transplant recipients were 10x less likely to get a diagnosis of dementia (assuming the same base rates). I would think because of their heavy interaction with the healthcare system they'd have a high rate of diagnosis.
Autoimmune issues may fit that bill in people with the right genetics. They can cause and/or contribute to CKD, which could push someone into kidney failure with other insults (eg dehydration), and can also contribute to dementia.
That would give us the opposite result, higher rates of dementia among organ transplants. It would have to be something that causes kidney failure, but prevents dementia.
How so? The autoimmunity would contribute to kidney failure when unchecked, and after failure and transplant, immunosuppressive meds would reduce the chances of developing dementia related to autoimmunity.
But according to this study, organ transplant patients have a much lower risk of dementia compared to the general population, not just people who have autoimmune diseases.
It could be that autoimmune activity/genetics, even if it doesn't result in a specific disease, contributes to certain aspects of dementia.
Take Celiac disease as an example. It only affects ~1% of the population, but ~30% of the population has the two genes (HLA-DQ2 and DQ8) that are most strongly associated with it and those genes are also associated with other autoimmune diseases.
There are similar thoughts with respect to the hygiene hypothesis and autoimmune/immune-related disease.
Other diseases, like Parkinson's, are also associated with autoimmune diseases. I suspect that there's some trade-off with respect to the effectiveness of the immune system/how well it deals with infections/cancer and the incidence of certain diseases/pathologies, but it's not something that's as straightforward as we would like it to be.
Or theoretically getting dementia a decade later could protect against organ failure a decade earlier.
But I really don't think that's it. If this data is right there is probably an effect. I agree with the author that the mostly likely reason this isn't true is because of bad data.