Association between Alzheimer's/Parkinson's diseases and cancers: Modifying effects of alcohol consumption and viral infections revealed by an ecological study

INTRODUCTION An inverse epidemiological association exists between Alzheimer's and Parkinson's diseases (AD/PD) and certain cancers. Using a sex‐stratified approach, this global study clarifies shared and distinct mechanisms underlying the complex AD/PD–cancer relationship. METHODS Data from two World Health Organization (WHO) databases were analyzed for correlations between AD/PD and 23 major cancers, stratified by sex, region, and etiology. RESULTS An inverse association was observed between AD/PD and most, especially gastrointestinal (GI), cancers. Conversely, virus‐related cancers including human papilloma virus (HPV)–driven cervical and hepatitis B virus (HBV)/hepatitis C virus (HCV)–related liver cancer (LC) were positively associated solely with PD, but not with AD. Sex‐specific analyses revealed distinct patterns: oesophagus cancer (OC) was positively correlated with AD/PD only in women. LC etiology showed opposing links to PD: HBV/HCV‐related positive and alcohol‐related inverse. Further analysis indicated alcohol exhibited contrasting roles: positive with GI cancers but inverse with AD/PD. DISCUSSION We provide novel epidemiological evidence on the complex interplay between neurodegeneration and cancers, suggesting shared biological pathways and modulators.