Reverse Causation, Physical Inactivity, and Dementia

One variable may influence another as cause and effect. However, in situations in which a cause-effect relationship is scientifically plausible, reverse causation may also be possible. As an example, physical inactivity may predispose to dementia through cardiometabolic and other mechanisms. However, physical inactivity may also be a result of an ongoing dementia prodrome in which patients are physically slowed down during the years preceding the dementia diagnosis. This article examines reverse causation and how it was studied in a recent individual participant data meta-analysis of physical inactivity as a risk factor for dementia. This article also shows that other interpretations are possible when a finding suggests reverse causation.