Dementia is a global problem and in this chapter we investigate modifiable protective and risk factors for dementia. The main question is when to intervene with preventative measures and which focus points should have priority to direct public health policies. Risk factors for vascular disease are also risk factors for dementia and should probably be addressed in midlife at the latest. We review evidence for the most optimal time of intervention for prevention of dementia when discussing protective and risk factors, with a focus on physical activity and cardiovascular risk factors. We also discuss other factors that may influence the relationship between physical activity and cognitive functioning and the implications for theory and practice.