Moderate-to-vigorous physical activity at any dose reduces dementia risk

In studies like this I always wonder if they have the causation reversed. Is the exercise staving off the dementia or are people who are healthy enough (mental and physical health) to exercise in the first place less likely to get dementia?

This headline is badly misleading . Traumatic and highly stressful moderate to vigorous physical raises dementia risk.

Manageable physical activity reduces dementia.

>> Each 30 minutes higher MVPA was associated with a 4% reduction in the risk of all-cause dementia

So 4% reduction means... complete chance of dementia? Or it helps 4 in 100 people? How can that be applied? I think that number lacks qualitative information. Conclusions like this are vague. I could see a number like 33% or 50% being more easily applied for expected results. 4% seems within a margin of error.