Evidence against a geographic gradient of Alzheimer's disease and the hygiene hypothesis

J Constance Lathe,Richard Lathe

doi:10.1093/emph/eoaa023

J Constance Lathe, Richard Lathe

Open Access

https://doi.org/10.1093/emph/eoaa023

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Abstract

A significant positive correlation was previously reported (Fox et al.Evol Med Public Health 2013; 2013:173–86) between hygiene and the global prevalence of Alzheimer's disease (AD) based on World Health Organization (2004) data. These data have now been updated by the Global Burden of Disease (GBD; 2016) dataset that takes into account under-registration and other potential confounds. We therefore addressed whether the association between hygiene and AD is maintained in light of these more recent data. We report a significant positive correlation between GBD AD prevalence rates and parasite burden, and a negative association with hygiene. These newer data argue that hygiene is not a risk factor for AD, and instead suggest that parasite burden may increase AD risk.Lay summary: It was previously hypothesized that hygeine might be a risk factor for the development of Alzheimer disease (AD), based on a global gradient of dementia. Newer data that correct global AD rates for under-reporting now demonstrate that parasite burden is positively correlated with AD.

Highlights

Fox et al [1] reported a significant positive correlation between hygiene and Alzheimer's disease (AD) prevalence across the world
To address whether the hygiene hypothesis is consistent with these more recent data, we studied whether the correlation observed by Fox et al is reproduced with the Global Burden of Disease (GBD) dataset
Whereas they observed a strong negative correlation, in which higher parasite burden was associated with reduced rates of AD (r = −0.61, p =

Summary

Introduction

Fox et al [1] reported a significant positive correlation between hygiene and AD prevalence across the world. Patient brain is reported to contain elevated levels of microbes, and the biomarker of the disease, Aβ, is likely to be a defense protein induced by infection, underlining the contention that microbial infection/reactivation might be causally linked to AD development [2,3] In this case, prior exposure to a diversity of environmental microbes might potentially protect against AD, whereas hygiene might increase the risk. Fox et al base their conclusions on correlations between measures of infection such as parasite stress versus per country rates of AD across the world, as reported by the World Health Organisation (WHO) in 2004 This dataset has been replaced by the Global Burden of Disease (GBD) dataset.

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