Cleanliness May Contribute to Alzheimer’s Risk

“The “hygiene hypothesis” suggests a relationship between cleaner environments and a higher risk of certain allergies and autoimmune diseases. Submitting that a lack of environmental microbial diversity may compromise proper immunoregulation, Molly Fox, from the University of Cambridge (United Kingdom), and colleagues suggest that people living in highly sanitized environments in developed nations have far less exposure to a diverse range of bacteria, viruses and other microorganisms – which may actually cause the immune system to develop poorly, exposing the brain to the inflammation associated with Alzheimer’s Disease. The researchers tested whether “pathogen prevalence” can explain the levels of variation in Alzheimer’s rates across 192 countries. After adjusting for differences in population age structures, the team found that countries with higher levels of sanitation had higher rates of Alzheimer’s: in countries where all people have access to clean drinking water, such as the UK and France, have 9% higher Alzheimer’s rates than countries where less than half have access, such as Kenya and Cambodia. Countries that have much lower rates of infectious disease, such as Switzerland and Iceland, have 12% higher rates of Alzheimer’s, as compared with countries with high rates of infectious disease, such as China and Ghana. More urbanized countries exhibited higher rates of Alzheimer’s, irrespective of life expectancy. Countries where more than three-quarters of the population are located in urban areas, such as the UK and Australia, exhibit 10% higher rates of Alzheimer’s compared to countries where less than one-tenth of people inhabit urban areas, such as Bangladesh and Nepal. Differences in levels of sanitation, infectious disease and urbanization accounted respectively for 33%, 36% and 28% of the discrepancy in Alzheimer’s rates between countries. Writing that: “Variation in hygiene may partly explain global patterns in [Alzheimer’s Disease] rates,” the study authors submit that: “Microorganism exposure may be inversely related to [Alzheimer’s Disease] risk. These results may help predict [Alzheimer’s Disease] burden in developing countries where microbial diversity is rapidly diminishing.”