Better hygiene may increase Alzheimer's risk

An obsession with cleanliness and hygiene could lead to a higher risk of developing Alzheimer's disease, Cambridge scientists have warned.
People living in industrialised countries may be more likely to develop Alzheimer's due to greatly reduced contact with bacteria, viruses and other microorganisms - which can lead to problems with immune development and increased risk of dementia, a new study claims.
The research found a "very significant" relationship between a nation's wealth and hygiene and the Alzheimer's "burden" on its population.
High-income, highly industrialised countries with large urban areas and better hygiene exhibit much higher rates of Alzheimer's, researchers said.

Using 'age-standardised' data - which predict Alzheimer's rates if all countries had the same population birth rate, life expectancy and age structure - the study found strong correlations between national sanitation levels and Alzheimer's.
This latest study adds further weight to the "hygiene hypothesis" in relation to Alzheimer's: that sanitised environments in developed nations result in far less exposure to a diverse range of bacteria, viruses and other microorganisms - which might actually cause the immune system to develop poorly, exposing the brain to the inflammation associated with Alzheimer's disease, researchers said.

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 study found that countries with higher levels of sanitation had higher rates of Alzheimer's.
For example, countries where all people have access to clean drinking water, such as the UK and France, have 9 per cent 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 per cent higher rates of Alzheimer's compared with countries with high rates of infectious disease, such as China and Ghana.
More urbanised 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 per cent 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 urbanisation accounted respectively for 33 per cent, 36 per cent and 28 per cent of the discrepancy in Alzheimer's rates between countries, researchers said.