Smaller families, higher dementia prevalence? A cross-national ecological study of fertility decline

Background Dementia prevalence is increasing globally and is most often examined in relation to population aging. Broader demographic patterns, including declining total fertility rates (TFR), may also be associated with between-country variation in dementia prevalence. This study examined the cross-national association between TFR and dementia prevalence rate per 100,000 population. Methods A cross-sectional ecological analysis was conducted using publicly available international datasets. TFR was examined as a country-level indicator of fertility regime and family-size structure. Descriptive statistics, scatterplot visualisation, bivariate and partial correlations, and pre-specified forced-entry multivariable regression models were used. Models adjusted for sex-specific aging/life expectancy, economic affluence, an exploratory country-level survivorship covariate, and urbanisation. Exploratory subgroup analyses were conducted across income, development, regional, and geopolitical classifications. Results Lower national TFR was consistently associated with higher dementia prevalence across total, male, and female populations. The five pre-specified predictors collectively accounted for 57.6%, 60.9%, and 56.4% of the variance in total, male, and female dementia prevalence, respectively. Temporal stability analyses showed that national TFR estimates from 1990 to 2012 were highly intercorrelated. Exploratory subgroup analyses suggested stronger inverse associations in low- and middle-income countries and developing country groupings. Conclusions This study identified a consistent country-level ecological association between lower TFR and higher dementia prevalence. The findings should not be interpreted as causal or individual-level evidence. Further longitudinal, multilevel, and individual-level research is needed to clarify demographic, social, caregiving, and health-system pathways.