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Life sciences · Journal article
Neurodegenerative Diseases · October 24, 2026
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Background: Poor social connection and ageing-related biological processes are recognised contributors to Alzheimer’s disease and related dementias. However, cross-national evidence linking structural indicators of social connection with dementia and broader neurological dis-ease burden remains limited. This ecological study examined country-level associations be-tween average household size and modelled neurological disease incidence estimates. Methods: Country- and territory-level data from up to 204 settings were analysed. Average household size was the primary exposure, and model-derived, age-standardised incidence-rate estimates for Alzheimer’s disease and other dementias were the primary outcome. Par-kinson’s disease, motor neuron disease, multiple sclerosis, idiopathic epilepsy, headache dis-orders, and total neurological disorders were examined as comparative secondary outcomes. The Henneberg Index, life expectancy at age 60, GDP per capita, and urban living were in-cluded as contextual covariates. Analyses included Pearson and Spearman correlations, par-tial correlations, principal component analysis, and multivariable linear regression. Results: Household size was strongly and inversely associated with Alzheimer’s disease and other dementias incidence estimates (Pearson r=−.841, p<.001). The association remained after adjustment for the included covariates (β=−.569, p<.001). Significant inverse adjusted associations were also observed for Parkinson’s disease, motor neuron disease, and total neurological disorders, whereas patterns differed for other neurological outcomes. Principal component analysis identified a single ageing–development dimension explaining 72.1% of the variance, with household size loading inversely against life expectancy at age 60, econom-ic affluence, urban living, and the Henneberg Index. Conclusion: Smaller average household size was associated with higher modelled incidence estimates for dementia and selected neurodegenerative diseases at the country level. These findings should be interpreted as ecological associations rather than evidence of individual-level causation and suggest that household structure is embedded within broader demograph-ic, socioeconomic, and ageing-related processes.