Largest-Ever Dementia Study: Exercise Cuts Risk 25%, Sitting 8+ Hours Daily Raises It 27%

The largest statistical analysis of lifestyle factors and dementia risk ever conducted has found that regular physical activity is associated with a 25% reduction in the probability of developing dementia, while sitting for eight or more hours per day is associated with a 27% increase — findings with immediate public health implications as global dementia rates are projected to triple by 2050. The study, a systematic review and meta-analysis published April 8, 2026 in the journal PLOS ONE, synthesized data from nearly five million participants across dozens of countries.

Researchers analyzed 49 studies covering 2,855,529 participants to quantify the protective effect of physical activity. The pooled relative risk was 0.75, with a 95% confidence interval of 0.68 to 0.82, meaning regular exercisers had a 25% lower probability of developing dementia compared to sedentary individuals after controlling for age, sex, and other health variables. The analysis included studies of aerobic exercise, resistance training, walking, and mixed activity regimens, and the protective association was consistent across study designs and geographic regions. The magnitude of the effect rivals or exceeds the benefit of most pharmacological interventions currently under development for dementia prevention.

The sedentary behavior findings came from a smaller set of three studies covering 295,809 participants, yielding a pooled relative risk of 1.27 — a 27% higher chance of dementia for people who sit eight or more hours per day. Crucially, the two findings are not simply mirror images of each other. Researchers found that even among people who meet exercise guidelines, prolonged uninterrupted sitting remained a meaningful risk factor, suggesting that the mechanism linking sedentary behavior to cognitive decline is at least partly independent of cardiovascular fitness.

The study also produced the most comprehensive analysis to date of sleep duration and dementia risk. Sleeping fewer than seven hours per night was associated with an 18% higher risk of dementia, while sleeping more than eight hours was associated with a 28% higher risk — a counterintuitive finding that researchers attributed partly to reverse causation, since early-stage dementia itself disrupts sleep architecture. The optimal window of seven to eight hours per night emerged as robustly protective in multiple independent study populations.

All three factors — physical activity, sedentary time, and sleep duration — are what researchers classify as modifiable, meaning the public can act on them without medical prescriptions or clinical intervention. "These are changes people can make today," said one of the study's lead researchers. Global dementia prevalence currently stands at roughly 55 million people, with an estimated 10 million new cases diagnosed annually. At the projected rate of increase, driven primarily by aging populations in Asia and sub-Saharan Africa, that number could reach 150 million by 2050.