Abstract
Alzheimer's disease (AD) shares certain etiological features with autoimmunity. Prevalence of autoimmunity varies between populations in accordance with variation in environmental microbial diversity. Exposure to microorganisms may improve individuals' immunoregulation in ways that protect against autoimmunity, and we suggest that this may also be the case for AD. Here, we investigate whether differences in microbial diversity can explain patterns of age-adjusted AD rates between countries. We use regression models to test whether pathogen prevalence, as a proxy for microbial diversity, across 192 countries can explain a significant amount of the variation in age-standardized AD disability-adjusted life-year (DALY) rates. We also review and assess the relationship between pathogen prevalence and AD rates in different world populations. Based on our analyses, it appears that hygiene is positively associated with AD risk. Countries with greater degree of sanitation and lower degree of pathogen prevalence have higher age-adjusted AD DALY rates. Countries with greater degree of urbanization and wealth exhibit higher age-adjusted AD DALY rates. Variation in hygiene may partly explain global patterns in AD rates. Microorganism exposure may be inversely related to AD risk. These results may help predict AD burden in developing countries where microbial diversity is rapidly diminishing. Epidemiological forecasting is important for preparing for future healthcare needs and research prioritization.
Highlights
Exposure to microorganisms is critical for the regulation of the immune system
disability-adjusted life-year (DALY) are calculated from years of lost life (YLL) and years lost due to disability (YLD)
Countries with higher disease and pathogen prevalence and Infant mortality rate’ (IMR) had lower 2004 Alzheimer’s disease (AD) rates (Table 1, Figs 1–4, Fig. S1). These results are consistent with a protective role of exposure to microbial diversity against AD, and support an hypothesis for Alzheimer’s disease (HHAD)
Summary
Exposure to microorganisms is critical for the regulation of the immune system. The immunodysregulation of autoimmunity has been associated with insufficient microorganism exposure [1]. Global incidence patterns of autoimmune diseases reflect this aspect of their etiology: autoimmunity is inversely correlated to microbial diversity [1, 2]. The similarity in immunobiology may lead to similarity in epidemiological patterns For this reason, here we test the hypothesis that AD incidence may be positively correlated to hygiene. We investigate whether differences in microbial diversity can explain patterns of age-adjusted AD rates between countries. Methodology: We use regression models to test whether pathogen prevalence, as a proxy for microbial diversity, across 192 countries can explain a significant amount of the variation in age-standardized AD disability-adjusted life-year (DALY) rates. Countries with greater degree of sanitation and lower degree of pathogen prevalence have higher age-adjusted AD DALY rates. Microorganism exposure may be inversely related to AD risk These results may help predict AD burden ß The Author(s) 2013.
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