Among 260,659 Korean cancer survivors followed for at least three years, those who maintained or increased physical activity after diagnosis had a 18% lower dementia risk (aHR 0.82, 95% CI 0.75–0.91) compared with those who sustained high activity levels, while those who decreased activity faced a 46% higher risk (aHR 1.46, 95% CI 1.31–1.62). Strikingly, the protective effect was concentrated in the chemotherapy-treated subgroup (aHR 0.80), with no significant association detected in non-chemotherapy patients.
This is a meaningful finding for the growing population of long-term cancer survivors — now numbering tens of millions globally. Chemotherapy-associated cognitive impairment ("chemo brain") is a documented phenomenon involving neuroinflammation, oxidative stress, and hippocampal damage, and exercise is mechanistically plausible as a countermeasure through BDNF upregulation and cerebrovascular improvement. The subgroup specificity here strengthens the biological story rather than weakening it.
Limitations are real: the retrospective, observational design cannot exclude residual confounding — sicker patients may both reduce activity and face higher dementia risk. Physical activity was self-reported via health screening questionnaires, and the Korean population may limit generalisability. Still, with a cohort of over a quarter-million and a clinically relevant stratification by treatment type, this qualifies as confirmatory-plus evidence. Oncologists and primary care physicians should treat post-treatment physical activity counselling as a cognitive-protection strategy, not merely a cardiovascular afterthought.
