A large systematic review and meta-analysis of prospective cohort studies found that among adults aged 35 years and older, higher physical activity, lower sedentary time, and sleeping 7–8 hours per night were associated with lower risk of incident dementia. Physical activity meeting recommended levels was linked to a 25% reduced risk (RR 0.75, 95% CI 0.68–0.82), while prolonged sedentary time (≥8 hours/day) and both short (<7 hours) and long (>8 hours) sleep were associated with increased risk. However, substantial heterogeneity, reliance on self-reported behaviors, and moderate-to-serious risk of bias mean these findings should be interpreted as associations rather than causal relationships.